1908. Bo WELL. — 0)1 the Anatomy of Vitrina pyrenaica. 97 



it is shrunk to very exiguous proportions ; and either in sections 

 orin dissections itspresence is at once indicated b3'staining with 

 dilute carbolthionin, which will of course colour everything 

 else in time, but goes first for the cells of which the peculiar 

 glandular structure of the flagellum is made up, just as borax 

 carmine serves as a histological test for the cells of the neph- 

 ridium, and may indeed on that account be turned to practical 

 use, since there are structures in the Neomeniidse concerning 

 which opinions differ as to whether the}^ are or are not neph- 

 ridia. I have observed the occasional atroph}' of the phallic 

 organs in other species ; for example, in Pyramidula 7upestris. 

 In this snail, according to my observations, the eggs seem to 

 be always retained in the body of the parent; and the young 

 snails do not come out until the parental structures are " de- 

 fecated to a pure transparency." This is the reason why so 

 man}^ vSpecimens of/*, ricpestris are found adhering to the rocks 

 on which they live, in a dried-up condition, and with their 

 periostracum rapidh' vanishing. On examining these speci- 

 mens I find them to contain eggs, or more commonly ^%'g 

 shells and j^oung snails ; the chief organs of the parent being 

 reduced to thin transparent membranes, the original functions 

 of which can, however, easil}^ be discerned; the radula of 

 course is in perfect condition. Being curious to know which 

 of the organs first suffered degeneration, I have looked care- 

 fully at others in which this process of encystment, if one may 

 be permitted to use the term, was apparently only beginning. 

 The glands of the digestive system appear shrunk, and the 

 male part of the genital apparatus is in an evanescent condi- 

 tion ; but the female epididymis and the albuminiparous glands 

 are well developed. The morphological interpretation of this 

 might be that in hermaphrodite Gastropods the male part of 

 the apparatus is secondary to the female part, an idea which 

 I find supported by such embr3'ological and developmental 

 facts as have come under my notice. I have some reason to 

 believe that the curious nidamental gland (a development of 

 the female epididymis) in lyimnoea is correlated with at? occa- 

 sional atavistic habit in gestation. I have found this gland 

 very large in large ovate specimens of Z,. pereggr ox vulgaris, 

 which occur .sparingl}^, in some seasons, in ponds where the 

 prevailing form is small and high-spired. I mention these 



