26o Records of the Indian Museum. {Yoh. XXII. 



Refractile Bodies. — Throughout the vascular parts of the 

 anatomy of the Viviparidae, and especially in the mantle, numer- 

 ous small refractile bodies can be distinguished under a low power 

 of the microscope. They are spherical or occasionally ellipsoidal 

 in form and become more numerous in the half-grown and adult 

 animal than they are in the young. Their size varies in different 

 species and they are largest (among the forms examined) in Lecy- 

 thoconcha key this. Unstained they are colourless, but they absorb 

 stains such as haematoxjdin and borax carmine readily and these 

 stains, if the bodies are cut in sections, penetrate throughout their 

 substance. They dissolve, however, immediately in acid and 

 therefore disappear in a technique in which the use of free acid is 

 involved, leaving open spaces that may easily be confused with 

 small blood-sinuses. Their position is extracellular, but they 

 occur in the peculiar gelatinous tissue described above. When the 

 mollusc is in a state of active growth thej' congregate in large 

 numbers between the shell-glands and the internal surface of the 

 mantle (fig. 14). Externallj' the}' are perfectly smooth. Their 

 internal structure is lamellar and concentric, but the lamellae of 

 which they are composed are not numerous. 



The structure of the shell-glands of both series is essentially 

 similar in the Melaniid genera Melanoides and Acrostoma to that 

 here described in the Viviparidae. As de Villepoix ' has shown 

 that it is also similar in Helix , we may assume that it is of a type 

 widely distributed among the Gasteropod molluscs. It will there- 

 fore be worth while, before discussing the function of the glands 

 and of the marginal region generally in relation to the ornamenta- 

 tion of the shell, to summarize the description already given so 

 far as its main points are concerned. I have been able to find no 

 detailed account of the external structure of this region, which 

 probably differs greatly in different forms, in any other family. 

 Even if certain features are peculiar to the Viviparidae, parallel, if 

 not precisely analogous, features probably exist in other families. 



Summary Account of the Ornamentation of the Shell. 



The ornamentation of the shell in the Viviparidae is partly 

 periostracal, partly impressed on the outer calcareous layers. In 

 the embryonic shell, including the protoconch, both horny and 

 testaceous structures are already concerned, but the periostracal 

 ornamentation, when magnified proportionately, is the more con- 

 spicuous. 



The periostracal ornamentation is, at any rate in some species, 

 both glyptic and coloured. Its sculpture is minute and consists 

 of spiral rows of horny chaetae, fine spiral ridges and still finer 

 oblique longitudinal lines. These are best developed in the fully- 

 formed embryo and as a rule disappear or become obsolete (with 

 the exception of the longitudinal lines, which tend to become more 



' de Villepoix, Comptes Rendus CXX, p. 512 1 1895). 



