268 BULLETIN OF THE 



have absolutely no connection with the body cavity at the time when 

 the glomerulus is formed, I could nevertheless defend my position by 

 the assumption that the blind anterior end of the duct is a compound 

 structure, representing both nephrostomal canal and pronephric cham- 

 ber. It seems to me that, were it necessary to make this assumption, 

 an extensive comparative study would justify such an interpretation. 



The pronephros of Teleosts was long supposed to remain functional 

 in the adult ; but recent investigations seem to favor the conclusion that 

 it never persists in fully mature individuals, with the possible exception 

 of a few degenerate animals like Fierasfer (cf. Balfour, SI**, '82 ; Grosglik, 

 '85 and '86; Emery, '80, '81, and '85 ; Calderwood, '91). 



The account given by Balfour and Parker ('82, pp. 415-424) of the 

 development of the pronephros in Lepidosteus is in very close agree- 

 ment with the development in Teleosts as described by Goette and by 

 Fiirbringer. The only conspicuous point of difference is, that, while in 

 Teleosts the pronephric chamber becomes wholly detached from the body 

 cavity, in Lepidosteus a remnant of the original communication probably 

 persists as a so-called peritoneal tubule. As among Teleosts, the pro- 

 nephros atrophies in adult Lepidostei. 



Beard's ('89, pp. 114, 115) account of the early development differs 

 greatly from that just given. According to this author, the pronephros 

 is formed as a solid proliferation from the intermediate cell layer 

 (Balfour) in the region from the 4th to the 8th or 9th somite inclusive. 

 Externally, the proliferation fuses with the ectoderm. As a rule, there 

 are formed three pairs of pronephric nephrostomes, of which the most 

 posterior pair abort. The pronephric chamber is formed by the narrow- 

 ing of the ciliated opening and the widening of the part opposite the 

 glomerulus. Since Beard does not describe the development of the 

 glomerulus, the account seems to me decidedly vague ; but I believe 

 I am right in accrediting to the author the view held by Hoffmann for 

 Teleosts, that the glomerulus is not developed in the body cavity. As 

 I understand him, it is develo])ed in the course of the pronephric 

 tubes. 



All the studies on Ganoids thus f^ir enumerated have been made upon 

 Lepidosteus. In Acipenser, Salensky ('78, '80) maintains, in opposition to 

 Kowalewsky, Owsjannikoff and Wagner ('70), that the excretory organs 

 first appear as a differentiation in the form of a solid cord of cells. There 

 is at that stage no trace of the coelom, nor of a division into protovertebral 

 and lateral plate. Indeed, this cord of cells first marks the region where 

 the latter separation will later occur. In its further development the 



