258 



Records of the Indian Museum. [Vol. XXII, 



tinguished, l^'ing in the external part of the vascular layer. Ex- 

 ternal to them, and not extending quite so far downwards or en- 

 tering the process, the calciferous glands occupy the whole of the 

 glandular area. These latter glands form in sections of the kind a 

 series of minute tubules with their main axis at right angles to the 

 surface, but a careful examination of a series of sections indicates 

 that the tubules are not really separate but form a continuous or 

 almost continuous tube with numerous closely adpressed loops. 

 The uppermost loops are already degenerating and do not stain well 

 and those quite near the margin are not closely adpressed and 

 have their cells smaller and probably not yet functional. In the 

 upper part of the marginal region, however, the glands are well 



KiG. 19. — Micniphutograph <;f a vertical section througli the anterior part of 

 the body of a young Vivit>ai'a confecfa just before birth, to show general position 

 of shell-glands. 



^./., gill-filaments; /., foot; w., mantle; m^, mouth; />,?., periostracal land; 

 gr.,radula; s.g., calciferous gland; sp. gr., supramarginal groove; 0./., operculi- 

 ferous lobe of foot 



developed and evidently functional. Here they consist of large 

 deeply staining cells arranged in parallel rows from just below the 

 external epithelium inwards to the base of the glandular layer. 



In the young of other species (fig. 19) the structure of these 

 glands is not essentially different, though they do not occupy 

 nearl}' so large an area and are relatively much smaller. Their 

 tubular conformation and the adpressed loops of the whole gland 

 are just as well marked and the cells are similar in form and ap- 

 pearance. 



At subsequent growth stages, however, a considerable change 

 takes place. The cells are greath'^ reduced in numbers but in- 

 creased in size and become ampulliform with extremely elongate 

 "necks" and swollen proximal parts. The loops of the primitive 

 gland, moreover are converted into groups of cells of the kind. 



