MOKPilOLOGY OF CYCLUöTOMATA. 395 



the embryos of Salmonidse, the earliest traces of the pronephros 

 consist, in embryos with 11 pairs of the somites, of five solid 

 proliferations of the lateral plate which is already cut off from 

 the somite. These proliferations, being coincident with the caudal 

 half of the third to seventh somites, are strictly metameric 

 in arranoement and are reofarded bv the author as the rudimentarv 

 pronephric tubules. These tubules soon become confluent with 

 one another to form a single outgrovvth of the lateral plate, which 

 is called by the author the " primäre Vornierenfalte." The 

 *' primäre Yornierenfalte," which passes over into the parietal and 

 visceral layers of the lateral plate, undergoes a longitudinal 

 constriction (the " sekundäre Vornierenfalte ") by which it is 

 divided into the dorsal and ventral parts. From the former, 

 the anterior section of the segmental duct originates, while the 

 latter is transformed into the pronephric chamber. By stages, 

 the dorsal part woanders laterally, and the ventral part travels 

 medianwards. At the same time, these parts are separated from 

 each other, leaving the communication at only one point, which 

 is called the " Pseudonephrostom." 



This phase of the development of the pronephros observed 

 by Felix is, as I believe, undoubtedly earlier than that looked 

 upon by the previous authors as the earliest indication of the 

 pronephros. 



At the time when the Anlagen of the pronephros are con- 

 verted into the " Vornierenfalte," the Anlage of the caudal contin- 

 uation of the segmental duct, becomes apparent in the eighth 

 to the tenth somite; it is brought about by the division of the 

 primary lateral plate (lateral plate in the ordinary sense) into (1) 

 the secondary lateral plate (lateral), (2) the segmental duct (middle), 

 and (3) the Anlage of the "Stammvenen" (median). This pro- 



