REPRODUCTIVE SYSTEM AND SEXUAL SUCCESSION OF L. BULIMOIDES 195 



In view of the probably uniform breeding season of the English Channel retroversa and the Ben- 



guela bulimoides, with but slight acceleration in summer, it is probable that variation in the rate of 



sexual succession is less pronounced in Limacina from warmer seas. Geographically, Limacina is 



divisible into two groups, the smaller-sized tropical species, trochiformis, inflata, lesueuri and bulimoides, 



HEIGHT OF SHELL IN MM. 



•5 1-4 1-3 1-2 I- 1 

 1 1 I I L 



09 



0-8 

 _L 



0:7 



06_ 



2-0 



-[ 1 1 1 r 



1-5 1-4 1-3 l-E H 



HEIGHT OF SHELL IN MM. 



Fig. 16. Diagram to summarize the course of the sexual succession of Limacina bulimoides. The topmost panel represents the 

 growth of the gonad, the scale showing the number of gonadial whorls. The successive stages in gametogenesis are indicated 

 by the types of shading. At the centre of the figure is shown the development of the male organs, as indicated by the epithelial 

 height of the prostate (see scale); and of the female tract, expressed by the cell height of the epithelium of the mucous gland. 

 Below is represented on the left the increase in size of the receptaculum seminis (total diameter, by the same scale), and the 

 increase in the number of whorls of the animal, gonadial whorls being represented in black. 



and the larger species of higher latitudes like retroversa (which extends also into the warmer parts of 

 the North Atlantic), balea, helicina and antarctica. The genus is well known to reach its highest 

 development, as indicated by the size attained by the species, in colder seas. It is probable that in 

 high latitudes the ' telescoping ' of the sexual succession, occurring in the summer months, may be 

 more advanced than the primitive condition of a fully extended sexual succession in warmer seas. For 

 example, in bulimoides 'telescoping' of the succession appears hardly to occur at all; but in cold water 



