Since the advent of nuclear fission, considerable interest has been aroused in the biological fate of strontium, as two isotopes of this element are among the longer-lived fission products of uranium. Strontium 90, in particular, constitutes the major hazard in old fission products because it is readily taken up by all kinds of plants and may then be concentrated in the bones of animals feeding on the plants. Strontium 90 contamination may be derived from fall-out from atomic explosions or from uncontrolled disposal of fission products. The oceans should receive more than twice as much Strontium 90 from fall-out as the continents because 70% of the surface area of the globe is covered by sea. The oceans are also used, though to a very limited extent at present, for the disposal of fission products from reactor wastes. Hence it is obviously important to study the behaviour of strontium in marine organisms in order to evaluate the health hazard caused by controlled or uncontrolled radioactive contamination of sea water. Barium has only relatively short-lived fission-product isotopes, but can readily be studied at the same time as strontium because of its similar chemistry.

During the autumn of 1954 plankton samples were taken in the northern Irish Sea and the North Channel from R.V. Clupea (Scottish Home Department) as part of a larger survey of the distribution of herring larvae. At the same period similar samples were taken in the central Irish Sea from R. V. William Herdman (Marine Biological Station, Port Erin). The present paper concerns the distribution, as shown by both sets of samples, of a few selected species.

I am indebted to all those on both vessels who assisted in taking the samples and to the Marine Laboratory, Aberdeen, for lending me for analysis the samples taken from R.V. Clupea.

The two new species, Gymnodinium vitiligo and G. veneficum, which are described below, are both small and highly motile, and in other respects very similar. The greatest difference between them is physiological, as G. vitiligo is harmless, whereas G. veneficum produces a very powerful toxin which is lethal to fish. There are also small morphological differences which are visible when the organisms are in culture, confirming the existence of two separate species.

On 30 July 1955 Dr J. H. Fraser, of the Scottish Home Department, Marine Laboratory, Aberdeen, sent to the British Museum for determination two adult females of a penaeid prawn collected at 01.56–02.0 h B.S.T. near the surface (15 fm.) at Rosemary Knoll, to the north-west of the Outer Hebrides, on 22 July 1955. The actual depth at this locality, 59° 12′ N., 10° 09′ W., is 229 fm (419 m). These specimens were identified by one of us (R. W. I.) as Funchalia woodwardi Johnson. Later the senior author confirmed this determination and wrote to Dr Fraser as follows:

Several methods have been devised for sampling plankton in the different water layers in the ocean, but for many years vertically hauled nets closed by a method devised by Nansen (1915) have fulfilled this purpose. Recently, however, an investigation by Barnes (1949) cast doubt on the validity of this method for quantitative work, and as in his paper he specifically referred to nets of the type used on the ‘Discovery’ Expeditions, the present observations were conducted to determine whether Barnes's findings were of general application to the method.

In a collection made with a 2 m stramin ring trawl at 47° 12′ N., 7° 40′ W. on 21 July 1955, with 450 fathoms of wire out, I have found two new species of medusae. These were each represented by a single specimen, one of which was an anthomedusa and the other a leptomedusa.

During a short visit of seven days to the Station Biologique, Roscoff, in June 1955, I was able to make some observations on living colonies of Merona cornucopiae (Norman) and on other hydroids. The object of my visit was to see living polyps of Tricyclusa singularis which were also found, but unexpectedly Merona was found during dredging and provided the opportunity for a much needed re-description from living material.

Little is known of the mechanisms whereby trematode parasites of fish gills attach themselves to their hosts. The adhesive apparatus consists of a posterior set of suckers or clamps supported by skeletal bars (sclerites) whose arrangement varies considerably in the different species. Yet though the pattern of these sclerites forms the main basis for the classification of the 200 or so species of the Diclidophoroidea into its six families, the only attempts to describe the mechanism of attachment of these parasites to their hosts appear to be those of Cerfontaine (1896), who described the attachment of Diclidophora denticulata to the gills of Gadus viretis, and of Sproston (1945a) and Llewellyn (1956a), both of whom described the attachment of Kuhnia scombri to the gills of Scomber scombrus. In the present paper the mechanism by which Plectanocotyle gurnardi (v. Ben. & Hesse) adheres to its hosts Trigla cuculus L., and T. lineata Gmelin will be described.

Experiments performed upon decapod crustaceans have produced much information on the hormonal control of moulting in this group. So far as I am aware, however, no one has tried to discover how moulting in other groups of Crustacea is controlled. This note represents the beginning of an attempt to investigate this aspect of moulting in the Isopoda.

It is well known that the smooth adductors of lamellibranch molluscs can hold the shells closed against the tension exerted by the elastic hinge ligament for prolonged periods without visible signs of fatigue. Two opposing hypotheses have been put forward to explain this phenomenon. One postulates that tonic contraction is a tetanic phenomenon and that the economy of lamellibranch smooth muscles is due to their slow speed of relaxation (Ritchie, 1928); whilst the other proposes the existence of a ‘catch mechanism’ which enables tension to be maintained without expenditure of energy, so that no excitation is needed during tonic contraction (Jordan, 1938).

Reports of recent attempts to discover how copper and mercury act as poisons to crustaceans are to be found in papers by Clarke (1947), Pyefinch & Mott (1948), Barnes & Stanbury (1948), Hoffmann (1950) and Russell Hunter (1950). Most of the evidence obtained has been interpreted in the light of two general theories (cf. Pyefinch & Mott, 1948). One is that these poisons exert their toxic effects by inactivating vital processes which occur at the animal's surface: the other is that they are absorbed by the animal and act internally by inhibiting metabolic changes. However, conclusive evidence supporting or excluding either possibility has yet to be obtained.

The vertical distribution of plankton organisms and their eggs depends largely on their surface area and density (Eyden, 1923). Gross & Raymont (1942) observed that the eggs of Calanus finmarchicus had a density (1.045–1.049 g/cc) greater than that of sea water (1.0235–1.025 g/cc), and that they sank at the rate of approximately 2.5 cm/min at 13°C. These workers pointed out that since the embryo takes 24 h to complete development, the eggs will sink in still water to a depth of 36 m before hatching and yet the data available, although not extensive, suggests that both eggs and nauplii are found most abundantly nearer the surface than this (Nicholls, 1933; Kraefft, 1910). If these observations are correct, then in addition to density and viscosity, there must be a third factor affecting the distribution of these eggs. Unfortunately, Gross & Raymont did not consider the possible effect of viscosity in their method for determining density, and they themselves commented on the disturbing degree of variation in some of their results. Their measurements of the rate of sinking of the eggs in sea water also showed considerable variation. It seemed worth while, therefore, to measure the density of these eggs using the density gradient technique of Linderstrøm-Lang (1937), a method which enables the individual and precise measurement of the density of small living objects, independent of their shape, i.e. surface area. This method was being used in work on Psammechinus eggs at the Marine Station, Millport, and, at the suggestion of Dr A. P. Orr, the following measurements were made on the eggs of Calanus finmarchicus.

In an age-frequency distribution plot of a biological population, it is axiomatic that there should be, in general, a preponderance of young. This expected distribution is not found when sampling some marine animals, notably lobsters and escallops. Many workers, including Priol (1930), Tang (1941), Elmhirst (1945), Baird (1952), Fairbridge (1953), and Mason have noted the absence ofyoung escallops (Pecten sp.) in the expected numbers in dredge hauls.

A dredge without teeth, lined with sprat netting, was used at Brixham in an attempt to catch the young escallops, but this dredge filled so quickly with sand, gravel and shell that very few escallops were caught, although those taken did have a generally lower size-range than the escallops caught with a standard toothed dredge. At Castletownbere (Co. Cork) a naturalist's dredge similarly failed to catch many escallops.

It has been well established that some of the features of the feeding and digestive process in molluscs are rhythmic in character. Notably Hirsch (1915, 1917, 1931) has demonstrated a rhythmic periodicity of secretion in the salivary glands and digestive glands of some carnivorous Gastropoda, and Krijgsman (1925, 1928) has done similar work on the land pulmonate Helix. In all of these animals—and in cephalopods, too, where there is a more elaborate nervous control of secretion—discontinuous feeding is the rule. In the other and perhaps larger category of molluscs—those continuously feeding on fine particles—the central mechanism of the gut is the crystalline style, or its forerunner the protostyle. Here the need is, in Yonge's words (1937), ‘to the extent to which they depend on extracellular enzymes for digestion, continuous secretion’. In Yonge's view, now classical, the style was regarded as ‘an ideal mechanism for the continuous liberation of small quantities of an amylolytic enzyme’. Graham (1939), in his work on style-bearing gastropods, showed that the style is in general confined to animals with a continuous feeding habit, whether by ciliary means or by using the radula to graze on and rasp off fine particles. It is known that style secretion stops and the style is frequentiy dissolved when animals are removed from the water and cease feeding (see Yonge, 1925).

Little is known about the food of the nauplii and early copepodite stages of copepods, although it has usually been assumed that the food particles must be smaller and perhaps more concentrated than for adults. A few observations have been made on the feeding of the young stages of Calanus in the laboratory, but none are available on feeding under natural conditions. It has been suggested (Marshall, Nicholls & Orr, 1934) that the success or failure of a brood of Calanus in the sea might depend on the presence of a rich food supply during its development. Experiments were therefore undertaken to find what organisms could be ingested by the nauplii and early copepodite stages, how much of the different foods could be digested, and how much water they could filter in a day.

In October 1921, a specimen of an echiuroid was taken in the otter trawl of the S.S. Salpa, in the neighbourhood of the Eddystone lighthouse. The specimen, a female, was provisionally identified by Mr E. Ford as Hamingia arctica Kör & Dan. The pharynx and uteri were opened in an unsuccessful search for males, after which the specimen was preserved in alcohol and put in the museum at the Plymouth Laboratory. In the following month, two more specimens were taken in the dredge by Dr R. S. Clark, a few miles from the same locality, and placed in the museum without further examination. No more specimens were obtained until April 1925, when one was taken in a trawl offRame Head, near the entrance to Plymouth Harbour. This specimen was examined by O. D. Hunt, and was found to be a female with uteri containing ripe eggs. Twenty-eight males of minute size were discovered attached externally to the female in a groove in the skin which extended for a short distance in the median line just posterior to what appeared to be a single genital orifice.

The presence in the sea of vitamin B12, or of its analogues, has been found necessary for the growth of several species of unicellular plants (e.g. Provasoli & Pintner, 1953; Droop, 1954, 1955).

Bioassays of the quantities in inshore waters during winter have been made by Lewin (1954) and by Droop (1954). The present investigation, carried out in 1955, was designed to extend this study and compare different seasons of the year.

The final regeneration stages of the nitrogen cycle in the sea are believed to consist of the bacterial oxidation of ammonium-nitrogen to nitrite and finally nitrate-nitrogen. There have been many attempts to demonstrate the presence in the sea of marine counterparts to the terrestrial Nitrosomonas and Nttrobacter. (See Zobell, 1946, for bibliography of the earlier work.) Bacteria which can oxidize either ammonia or nitrite are easily demonstrated in samples of bottom material or water contaminated by land drainage or bottom deposits. On the other hand, there has been general failure to demonstrate the presence of such species in the upper layers of the open ocean.

Isolated individuals of certain species of cirripedes are known to remain unfertilized at the time when the majority of contiguous individuals are carrying egg masses. From a very large number of observations on both Balanus balanoides (L.) and Elminius modestus Darwin (Crisp, 1950, 1956) there remains little doubt that in these two species copulation is necessary before eggs are brought into the mantle cavity where they are fertilized. Though fewer field observations have been made, Balanus crenatus Bruguière appears to behave similarly, isolated specimens grown on raft-exposed panels never bearing fertilized egg masses (Crisp, 1950; Barnes, unpublished observation). B. balanus (L.) (= B. porcatus da Costa) is also in all probability an obligatory cross-fertilizing hermaphrodite, though the available evidence does not exclude the possibility of self-fertilization in rare instances (Crisp, 1954; Barnes & Barnes, 1954).