1920.] E. Ghosh : Anatomy of the Solenidae. 73 



crystalline style. The question arises whether the coecum of the 

 crystalline style has primarih- originated from the side of the 

 intestine as a side groove and has only secondarily separated 

 from it to form a distinct and separate tube, or the coecum has 

 primarily arisen as a ventral outgrowth of the stomach and has 

 only secondarily acquired a connection with the intestine by the 

 fusion of their walls. The researches of Barrois (2) have conclu- 

 sively shown that the epithelial structure of the coecum of the 

 crystalline style and intestine are quite different from each other 

 whether the^' are fused together or not. Lately Bloomer has arrived 

 at a similar conclusion, also corroborated by ray own histological 

 study on Neosoleii and N ovaculina . 



M. Martin {Jenaisch. fur Naturwiss. LH, 1914, pp. 363-444) 

 has studied the relation of the crystalline style with the in- 

 testine and has found that the coecum of the crystalline style 

 and the beginning of the intestine form together a single short 

 wide tube in Nucula and in many Filibranchia. Hence, the 

 condition found in one of the primitive t^^pes of Pelecypoda 

 may be considered primarily at least in the present class. But 

 it is quite probable that the condition might have arisen from 

 one with a coecum distinct and separate from the intestine, 

 as is still found in many Prosobranchia, and which was perhaps 

 present in the ancestral forms before the evolution of the present 

 class. The peculiar condition in the subfam. Solecurtinae may 

 be easily derived from that found in Nticula simply by the 

 elongation of the short conjoined portion into a long narrow tube, 

 otherwise retaining the same primitive stage. The coeca of 

 N ovaculina and of the subfam. Soleninae differ from the above 

 primitive type in being separate and distinct from the intestine. 

 But the case of N ovaculina seems to be dift'erent in origin from 

 that of the members of the Soleninae. In N ovaculina , the coecum 

 seems to have separated at an early stage from the intestine, and 

 in the process might have passed through a stage still found in 

 Modiolaria (see Martin's paper). In the Soleninae, the condition 

 has arisen at a later epoch secondarily from that of the Sole- 

 curtinae. The presence of connective tissue uniting the walls of 

 the coecum and intestine, as distinctly shown by Bloomer, may be 

 set forth as strong evidence for such a hypothesis, viz, the 

 separation of the wall of the coecum from the intestine has taken 

 place secondarily from a condition seen at present in the members 

 of the Solecurtinae, the connective tissue being left as the last 

 remnant of a former continuity of the two. Consequently it 

 might be argued that the ancestral forms of the subfam. Soleninae 

 have arisen from one with the intestine and coecum fused together 

 (as in all Solecurtinae), but still without the development of a 

 cruciform muscle, there being not a trace of it in the subfam. 

 Soleninae ; they then acquired the lateral flattening of the bod)^ 

 and lost the connection between the coecum and intestine. It is 

 also probable that the ancestral forms of both the subfamilies had 

 their mantle lobes free along their ventral margins or just con- 



