578 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



be exclusively excretory, the usual condition, or mainly genital 

 (Solenogastra), or genito-urinary. 



Development of the Adult Nephridia. — According to one view 

 the glandular portion of the nephridium arises as a peritoneal funnel, 

 an evagination of the pericardium, this joining later with an ecto- 

 blastic ingrowth, the duct or ureter; in support of this view is the 

 work of Rabl (1879, Planorbis), Erlanger (1891a, Paludina), 

 Biitschli (1877, Paludina), Salensky (1885, Fcrnietus), Schimke- 

 witsch (1888, Lf;na.i-), Drummond (1902, Fa/Mdmo), Ahting (1901, 

 Pelecypods), Pelseneer (1901, Helix), and Stauffacher (1898, 

 Cyclas). That these organs are wholly mesoblastic is the opinion 

 of Salensky (1872, Calyptraa), Erlanger (1892&, Bythinia), 

 Georgevitch (1900, Aplysia), and Faussek (1900, Loligo). The 

 third view is that they are altogether ectoblastic: Fol (1875, Ptero- 

 pods), Bobretzky (1877, Nassa), Joyeux-Laffuie (1882, Onchid- 

 iuni), Sarasin (1882, Bythinia), and Meisenheimer (1898, Limax, 

 1901a, Dreissensia, 1901&, Cyclas). 



The first of these views has the greatest support, pointing to the 

 pericardial origin of the funnel and glandular portion, and to ecto- 

 blastic origin of some portion of the ureter only. For the third 

 view, wholly ectoblastic origin, it will be noted that the only recent 

 work is that of Meisenheimer. Now almost all the writers con- 

 clude a common origin of the glandular portion of the nephridium 

 and the pericardium and Meisenheimer does so likewise, but in 

 opposition to almost all preceding study he regards the pericardium 

 and heart as ectoblastic abstrictions. Meisenheimer must surely be 

 incorrect in interpreting the peritoneum and with it the nephridium 

 as ectoblastic, /. c., he must have defined the germ layers quite differ- 

 ently from other embryologists, since the pericardial cavity is justly 

 considered coelomic yet in no other animal group is the coelom re- 

 garded as lined by ectoblast. 



These definitive nephridia seem to arise independently of the 

 larval ones, save that Rho (1888) and MazzarelH (1892, 1898) state 

 that the mesoblastic anal kidneys of opisthobranch larvae become 

 transformed into the adult ones. 



Genital Ducts. — " Relations between the nephridial and genital 

 system, similar to those in the Worms, exist in the Solenogastrids 



