The great importance of lice as parasites and vectors of disease in man led one of us (Nuttall), soon after the outbreak of the Great War, to undertake a detailed study of these insects. It was known, prior to the war (1909–14), that lice transmit typhus and relapsing fever and during the war (1917–18) it was established that they also serve as vectors of trench fever. Beginning with February 1917, a number of papers dealing with various aspects of the louse problem were published in Parasitology (see vols. X–XIII), the study of their structure, systematics and biology being actively pursued whilst the best methods of combating them were sought for with a view to aiding the armies in the field. Of these papers, that dealing with the structure and function of the genitalia in Pediculus (II, 1917) bears directly on the subjects to which this Iconography relates.

The stem infestation of Oscinella frit in England is attacked by at least two species of hymenopterous parasites of considerable importance. The species are Halticoptera fuscicornis Walk. (Chalcidoidea) and Rhoptromeris eucera Htg. (Cynipoidea). It is also parasitised to a much lesser degree by Loxotropa tritoma Thoms. (Proctotrypoidea). These three species are described and figured in detail.

The three species named above have been reared by the writer from host puparia obtained in the Harpenden district; they have also been reared in the Leeds and Oxford districts by other observers. They attack the host in the larval stage of the latter and emerge from the puparia. All three species are characteristic parasites of cyclorrhaphous Diptera.

In the Harpenden district a parasitism of 27 per cent. was observed in 1926 and of 37 per cent. in 1927, Rhoptromeris eucera being the dominant parasite.

Evidence is brought forward which appears to indicate that the parasites, collectively, become more abundant as the season advances, with the result that Oscinella frit affecting late sown oats suffers markedly heavier parasitisation than when it attacks oats drilled earlier in the season.

The time of maximum emergence of Oscinella frit in out-of-door rearing cages during the years 1926 and 1927 coincided very closely with its period of greatest abundance in the field, as recorded by Cunliffe.

1. A new variety of the trematode Harmostomum opisthotrias is reported from the North American opossum.

2. Body proportions in this genus are more constant than linear dimensions and are, therefore, considered more desirable as a basis for taxonomic distinctions.

3. The occurrence of this parasite in a host with a range as limited and a phylogenetic position as critical as that of the opossums suggests the possibility of valuable information to be obtained through host-parasite relationship studies in this group. Investigators who are working with this material should keep the problem in mind.

A detailed description of the anatomy of the proboscis of the blow-fly, C. erythrocephala, and of the functions of the structures found in it is given. Attention is particularly directed to the fact that the fly can feed in several ways. It can filter the larger particles out of its liquid food, or can scrape chosen surfaces, moistened with vomit or saliva, with its prestomal teeth and subsequently ingest the emulsion produced, or can suck up materials, such as thick sputum or faeces containing helminth ova, without the intervention of its filtering apparatus or the application of its teeth. The relation of these modes of feeding to infection is very briefly indicated.

There have been described in detail adaptations of dilution egg counting and direct centrifugal flotation for use on sheep faeces for the ova of Haemonchus contortus, together with certain data on their comparative efficiency. It is suggested that extension of the methods as given, or with appropriate modifications, would permit studies from a variety of angles on the helminthic infestations of the gastro-intestinal tract and its diverticula among domestic animals.

In February 1928 I obtained from a ♂ Scyllium canicula, taken at Plymouth, a ♀ Lernaeopoda scyllicola bearing a younger and better preserved male than any I had hitherto observed. It is the first time in this genus that a male has been found anywhere other than on the female's shoulder, namely on one of the abdominal appendages, and the male was probably alive at the moment of fixation. The heads of the sexes point in opposite directions so that in Fig. 1 the abdominal appendage is “upside down,” and the genital process of the male is near a vulva of the female which is however fertilised since it bears egg-strings. I am now fortunate in having the kind services of Miss E. C. Humphreys to illustrate this male which is not shrunk into its carapace and desire that Figs 1. and 2 shall supersede my figures of 1918. The near second maxilla has been omitted to show the method of attachment of the male.

Pp. 183–4. The specific names of the parasite and the host should be transposed.

P. 277. Legend to Fig. 5, for dubius, read bicaudatus.

Three lines from bottom of page, for ♂♂, read ♀♀.

Material. On 28. V. 1928 two females of Brachiella merluccii Bassett-Smith, 1896 were taken by the author from the tips of the gill-rakers of a single Merluccisu vulgaris at Plymouth. One of these was accompanied by a male upon the cephalothorax. The female is generally well known, but there is no complete account of the appendages of the male.