212 



The Gonocytes then, frequently avail themselves of the nephro- 

 stomes and coelomic pores to dehisce to the exterior, so that there is 

 ground for believing that the ek-phorocytes, of similar origin and fate, 

 follow the same course and are discharged through the coelomic pores 

 or nephrostomes. 



3) In several of the most important animal types there is ground 

 for believing that the nephridia have never existed and in some at 

 least of these, e. g., Echinoderma, we have seen that it is easy to de- 

 monstrate that the egestive cells find their way to the exterior at other 

 parts of the organism 3^^ but in others there is ontogenetic evidence 

 that the nephridia, or at least the nephrostomes have atrophied. 



Amongst these may be noted: 1) The Arthropoda; 2) The Verte- 

 brata; 3) The Polyzoa. 



1) The Arthropoda. If we assume the above hypothesis with 

 regard to the function of the nephrostomes, we must also assume that 

 in the case of atrophy of the nephrostomes, the egestive cells must 

 either cease to leave the organism or must find an exit elsewhere. Yet 

 another alternative there is, that the immigration of egestive cells is 

 checked. As above alluded to, the elaboration of the polycytic dige- 

 stive processes causes a correlative disappearance of the monocytic 

 mechanical ingestion and hence also a disappearance of the monocytic 

 egestion. The development of digestive glands, salivary, and hepatic, 

 in the Arthropoda may thus be the indirect causes of the atrophy 

 of the nephrostomes, so that excretion only is efi"ected by the 

 closed green glands, shell glands and malpighian tubules ^s. Ege- 

 stive processes do, however, no doubt exist. Thus if foreign bodies be 

 introduced into the »body cavity« of insects 3^, they are taken up by 

 wandering cells and are deposited in certain parts of the organism, 

 more or less permanently. 



The Arthropoda will be later referred to again. 



2) The Vertebrata. In this group it has been shewn that there 

 is a gradual diff"erentiation of the glandular elements of the intestine 

 and a corresponding reduction of the mechanical (monocytic) ingestive 

 processes-^''. (Schäfer, Wiedersheim.) 



In an exact correlation to this, the nephrostomial funnels become 

 atrophied, so that in the Sauropsida and Mammalia the funnels do not 

 appear appreciably to perform an active function in the whole life of 



3* I leave out of consideration the disputed homology of the dorsal organ. 



35 Kowalevsky, Biol. Centralblatt. Bd. IX. 



36 H. E. Durham, Q. J. M. S. XXXIII. 



3^ R. W i e d e r S h e i m, loc. cit. und Über die mechan. Aufnahme der Nahrungs- 

 mittel in der Darmschleimhaut. Festschr. Vers, deutsch. Naturforsch, u. Arzte Frei- 

 burg 1883. — A. E. S c h ä f e r , loc. cit. 



