No. 6(l92l) COMMON MOLLUSCS OF SOUTH INDIA 12/ 



sea-water to provide the aeration needed by the larvae. The 

 horizontal partitions or walls are much thinner than the outer or 

 circular wall of the capsule. 



In each chamber or capsule a considerable number of fertilized 

 ova are deposited, embedded in a transparent, colourless, albumin- 

 ous nutritive jelly which entirely fills the chamber. In this matrix 

 the embryos go quickly through the trochosphere stage and then 

 assume a modified veliger form characterized by the possession of 

 a s])iral larval shell. This is quite different from that of the adult 

 and is distinguished by the term protocoiich. In its full develop- 

 ment it reaches a length of about a quarter of an inch ; the whorls 

 are all nearly the same diameter, so that it appears when fully 

 formed as a cylindrical coil of about 2^ to 3 turns. During the 

 earlier larval period fratricidal war occurs among the brood, 

 ending in the disappearance of the weaker among them, till only 

 some half dozen (5 to 7 usually) remain alive to complete their 

 development within the capsule. The change to the miniature 

 semblance of the adult takes place suddenly ; there is no grada- 

 tion from the cylindrical form of the protoconch into that of the 

 young adult form marked by the expansion of the mouth whorl, 

 an expansion that widens continuously to keep pace with the 

 rapid increase in size of the young chank. Differences of colour 

 and surface also take place ; from the white smooth surface of the 

 protoconch, the newer part of the shell becomes brown-flecked, 

 with a distinctly angular shoulder, bearing low knobs 



By the time the young chanks attain a length of rather over 

 half an inch, all the nutritive contents of the capsule have been 

 exhausted, and being no longer able to devour one another because 

 of the stoutness of their shell, the ravenous young find it necessary 

 to leave home in search of food. Their first step is to eat through 

 the partitions dividing the separate chambers, a proceeding which 

 results in the bringing together of the whole surviving family, 

 numbering usually from 200 to 250 in all. The stronger next 

 either eat a way through the outer wall or force their way out 

 between the capsules. The whole brood follow, to scatter over the 

 adjacent sea-bottom to lead independent lives. It is noteworthy 

 that in the chank, the protoconch persists through life, accidents 

 excepted, at the apex of the adult shell. 



