84 H. J. FLEITRE. 



his conclusions by observations on the " renal gland." He 

 brings forward much evidence in favour of considering this 

 gland^ so generally found in Tsenioglossa, as a modified vestige 

 of the left kidney which has become intimately connected 

 with the " pericardial gland." This gland consists of tubules 

 which are lined by ciliated epithelium and open into the renal 

 cavity (see fig. 9, h). The absence of this renal gland from the 

 primitive Paludina suggests the hope that further work will 

 reveal traces of the old left kidney in a less modified condi- 

 tion. The probability that further work will result in the 

 discovery of the above-mentioned interrenal connection in 

 other forms is increased by the fact that such connections 

 .are by no means unusual in Mollusca. They exist in several 

 Lamellibranchs and in Cephalopods^ and, without presuming 

 to suggest that they are homologous throughout, their occur- 

 rence diminishes the improbability of their occurrence in 

 Gastropods. 



The remaining problem is the derivation of the accessory 

 reproductive organs of the Tsenioglossa and of their descend- 

 ants the Opisthobranchs and Pulmonates. 



The male has, typically, a large penis (r) at the right side 

 of the head ; this organ is retractile in more primitive forms 

 (Paludina, fig. 8), but permanently extruded, in more special- 

 ised forms (Buccinum, fig. 10). A very similar structure is 

 found in the hermaphrodite Opisthobranchs, though their 

 hermaphroditism has been shown by Pelseneer (10) to be due 

 to the development of a male gonad in the female. 



Mr. J. E. S. Moore (12) found an archaic form in Lake 

 Tanganyika, which he named after its abode — Tangan- 

 yikia rufofilosa. The female of this animal possesses a 

 brood pouch (b. p., fig. 5, o) on the left side of the head in the 

 position of the penis of a male Paludina. He found the same 

 structure in Melania episcopalis, and both also possessed 

 a groove connecting this pouch with the genital aperture. 

 This strongly resembles the spermatic grooves of some 

 Opisthobranchs, and similar grooves also exist in the females 

 of some Taiuioglossa (figs. 8 and 9), while in the males the 



