Seasonal changes in the distribution of Lymnœa peregra (Müller) on a gently sloping beach of Loch Lomond have been studied in detail, with particular reference to the effects of the changes in water level which occur. At lower water temperatures the distribution can be correlated with the availability of food. At higher water temperatures the respiratory needs of adult snails cause them to remain close to the water's edge, even in the absence of food. This is not always true of young snails. Measurement of the fæces produced by such adult snails gives further evidence that a degree of starvation can occur for short periods in the summer months.

Comparative data on the characteristics of the physical environment and the general distribution of gastropods in Loch Lomond are given, and the study discussed in relation to previous work on the littoral ecology of large lakes.

The passage of ova down the Fallopian tube and uterine horn of one side into the horn of the other side is generally referred to as transuterine migration. There is evidence that such transmigration can occur in a wide variety of animals—Ungulata, Carnivora, Cheiroptera, Insectivora and Primates (Boyd, Hamilton and Hammond, 1944; Marshall's Physiology of Reproduction, 1952). In all these forms the genital tract has a single supravaginal segment varying from a common cervical canal to the single uterine cavity of the primate uterus simplex. The uterus of the albino rat is generally described as “uterus duplex”, with separate cervical canals opening independently into the vagina, and it has been stated by Hanson and Boone (1925, 1926) and by Slonaker (1927) that there is no evidence that transuterine migration occurs in the albino rat. In the course of an experimental investigation of the vascular pattern in pregnancy in the rat, some results were obtained which indicate that transuterine migration can occur in the albino rat.

In the Caridea, unlike the allied Euphausiacea and Penæidea, developing eggs are attached by means of a “cement” to specialized non-pinnate ovigerous setæ on pleopods 1–4; in Crangon also to periopods 4 and 5. The presence of these eggs does not prevent flexure of the abdomen and execution of backward escape movements. The form of the abdomen differs in relation to habit, and this, together with the disposition of the ovigerous setæ, which varies greatly in different genera and in different pleopods of the same species, conditions the arrangement of the egg-mass. Ovigerous setæ increase both in numbers and in length with age; so do the number of eggs which have to be attached. There is concentration in the pleopods of “cement” glands identical with the tegumental glands which secrete the epicuticle which the “cement” resembles in all respects. Ducts run into the ovigerous setæ but it remains obscure where the “cement” emerges; possibly it dissolves its way through the integument of the setæ to emerge at many places simultaneously. Attachment of eggs in the Caridea may be associated with the many different habits exhibited; the developing eggs are protected and hatch out in the often restricted environment of the parent.

The colour-pattern of hybrids between Ara chloroptera male and Ara ararauna female (Aves, Psittaci) combines parental features with a character which is found in some more “primitive” species of the genus but does not occur in the two parent species. The anatomical significance of this “ancestral” pattern mark is discussed.