I92I.J N. Annandale & R. B. S. Sew ell : Vivipara. 251 



pletely in the adult of T'. dissimilis and L. lecythis, so long as I ex- 

 amined only preserved material ; but at am- rate the three primary 

 processes can be quite easily detected in the largest living indi- 

 viduals of the former species, while in full grown specimens of the 

 Lecythoconcha, at least traces of the peripheral process sometimes 

 persist and probably remain functional throughout life. In L. lecy- 

 this (fig. 13) the primary processes are very conspicuous for at least 

 a fortnight after birth on account of their bright yellow colour as 

 well as their prominence. Major Sewell (p. 220) has shown that 

 even when the processes have apparenth' disappeared in V. bengal- 

 ensis their position is apparently indicated by streaks of yellow 

 pigment. In V. oxytropis both the primary and the secondary pro- 

 cesses increase in actual size with the growth of the animal. In 

 the living adult they are not so easily seen as the primary proces- 

 ses in the young of Lecylhoconcha, because they are usually retro- 

 verted inside the shell when the animal is expanded, but even in 

 material preserved by immersion in strong spirit and killed in a 

 highly contracted condition, they can be detected without difficulty 

 as soon as the shell is removed. 



The fact seems to be, therefore, that these marginal processes 

 are characteristic of the Viviparidae as a family. They differ 

 in position and structure, and probablj' in function, from the pro- 

 cesses present on the mantle of certain genera of Melaniidae,' and 

 I have failed to trace them on that of any Hj^drobiid. Their 

 presence is, however, frequently concealed by contraction and 

 shrinkage in preserved specimens, and the extent to which they 

 actualljr degenerate or persist in the adult differs in different 

 species. 



Other questions that remain to be answered are those con- 

 cerned with differences in the sj'stem of marginal and supramarginal 

 grooves and in the supramarginal ridge at different periods in the 

 life-history of the mollusc. What I have said of the marginal 

 processes applies with equal force to the marginal grooves, except 

 that in the adult of Lecyihoconcha the peripheral marginal groove 

 is sometimes still more distinct than the peripheral process, but 

 in considering the subsequent history of the supramarginal groove 

 another factor must be considered, viz. that of periods of growth 

 and of rest. These affect the groove indirectly by affecting the 

 ridge that lies immediately above it and can be discussed most 

 conveniently when considering the internal structure of this ridge 

 (p. 252). One point that may be noted here is that the cilia dis- 

 appear from the surface of the ridge at an early period in post- 

 embryonic life and that when the glands in it are in a state of 

 activity its surface is minutely ridged at right angles to its own 

 axis. Further, in growing specimens of Taia intha, preserved in a 

 half-expanded state, the ridge bears cushion-shaped swellings oppo- 

 site to, but much broader than, the primary processes. 



1 See Benson, Gleanings in Science I, p. 21 (1830), and .Annandale, Rec.Ind. 

 Mits. XIX, p. 109 (1920). 



