IV. 



Recent Progress in Conchology. 



SOME recently-published conchological treatises seem deserving of 

 somewhat more than a mere passing notice in these pages, since 

 they contain matter which deals with either the whole, or a large 

 section, of the molluscan phylum. 



To begin with, there is an interesting paper from the pen of 

 M. Moynier de Villepoix (i) that furnishes an admirable summary of 

 what is known concerning the formation and growth of the molluscan 

 shell. It is not, however, confined to a summary, and among the new 

 points which its author claims to have established is the mode of for- 

 mation of the ligament in bivalves. This, it appears, is secreted by the 

 epithelium of the dorsal suture, each of its constituent elements being 

 formed by cells specialised for the purpose. With regard to his 

 observations on the growth of the shell in Helix, we greatly fear that 

 those relating to the special areas of secretion of the mantle, with the 

 description of their cells, will have to rank as confirmatory only and not 

 as discoveries, for if we mistake not these structures have already 

 been dealt with some years ago by MM. Longe and Mer (2), the title 

 of whose paper we miss from the valuable bibliography at the end of 

 the memoir. Two other references seem also to have escaped the 

 vigilance of the writer, namely Gray's principal and important paper 

 on shell-structure (3), and the source of that naturalist's inspiration 

 (albeit unacknowledged), Count Bournon's work on Calcite (4). 



The next memoir to which we wish to allude is that by M. H. 

 Fischer (5), a coming writer on molluscan anatomy and already noted 

 for the careful nature of his work, who deals in a comprehensive 

 manner with the morphology of the liver in the Gastropoda. 



His principal results may be briefly summarised as follows : — In 

 the Scutibranchs (e.g., Neviiina) the hepatic lobes of the embryo are 

 equal and symmetrical. One genus only of the Prosobranchs, Valvata, 

 which also resembles the Scutibranchs in possessing a bipectinate 

 gill, displays the same regularity. In all other Gastropods the two 

 lobes are unequal, either ab initio or soon after their formation, the left 

 lobe being the larger. It sometimes happens in the adult (Elysia, 

 Avion, Buccinum) that the balance is restored, but this acquired sym- 

 metry of a later stage has not the same morphological value that 

 attaches to a like equality in the initial stages of the development of 



d 2 



