1908.] ASPIDOBRAXCH GASTROPOD MOLLUSCS. 823 



inclined to identify with the subpallial sensory tracts of Patellidfe, 

 &c., rather than with a true osphiadium ; the left columellar 

 muscle, which he considers to be derived from the subdivision of 

 the primitive right muscle ; the salivary glands, iu resjject of 

 which he corrects the statements of Haller and Amaudrut, Thiele 

 proceeds to give a more detailed account of the accessory genital 

 organs. Though his diagiams are too schematic, his drawings of 

 sections too few in number, and his description too condensed 

 to convey a clear impression to anyone unfamiliar with these 

 complex structures, his account of the female organs of Nerita pica 

 and Septaria parva is very exact, both as regards the general 

 anatomy and the histology. I shall have occasion to refer 

 frequently to it in the descriptive part of this paper. It need 

 only be mentioned here that he does not appear to have found 

 sperm atophores in the spermatophore-sac, and therefore is obscure 

 as to the function of this organ. Though he found and has 

 figured the peculiar crystalline concretions in the crystal-sac, he 

 names this structure the uterus — for insufficient reasons, as it 

 appears to me. He did nob discover the oviduco-coelomic funnel, 

 and does not mention the presence of the third duct, which I have 

 called the ductus enigmaticus in Septaria parva. It is of course 

 possible that it is not present in this species. The description of 

 the female organs of Scutellina cinnamomea leaves no doubt that 

 this form is a member of the Neritidaj. The description of the 

 male organs of Helicina japonica will be dealt with in the second 

 part of this paper, and I can supplement it by an account of the 

 female organs of Alcadia. Thiele regards the " receptaculum 

 seminis," i. e. the spermatophore-sac, as the representative of the 

 right kidney in female Neritidfe, and though I do not agree with 

 this conclusion it is not far from the truth. 



Further on Thiele gives a description of the kidney in Xerita 

 jnca and in Septaria, and here also makes more accurate obser- 

 vations than any of his predecessors. He also notices the 

 extension of the pericardial cavity to the right side of the animal 

 in Septaria, and makes a. juist comparison between the conditions 

 obtaining in this animal and the Cephalopoda. In conclusion, 

 Thiele suggests that the Neritidfe may haA^e been derived from 

 the Trochida?, but points out features in which they show a 

 resemblance to the Docoglossa. The lattei-, however, as he says, 

 are more probably analogies than homologies, as the radula and 

 the structure of the generative organs preclude any idea of close 

 relationship between these groups. 



The genus Neritina, owing to the abundance of the common 

 N . jiiiviatills in European rivers, has been more often and more 

 thoroughly studied than the genus Nerita. It is not necessary 

 to do more than refer to the works of Mocjuin-Tandon (38), 

 Claparede (12), and Landsberg (24), or to the paper on the develop- 

 ment of Xeritina by Blochmann (4), because the results obtained 

 by these authors have already been discussed and entirely super- 

 seded by the admirable papers of Lenssen (25 k, 26). In the first 



