286 BULLETIN OF THE 



ventral portion of the broad pronephric thickening. Mollier's descrip- 

 tion is substantially in accord with my own observations, and it seems 

 to me probable that Kellogg's statements are to be understood in the 

 same way. 



The structure of the functional pronephros was early the occasion of 

 much controversy. The discoverer of the organ, Joh. Muller ('29 and 

 '30), describes and figures it as a cluster of blind tubules, which radiate 

 in the form of a rosette from the anterior tip of the segmental duct. 

 This view was shared by the larger number of the early investigators. 

 According to von Wittich ('52), the gland is typically formed by the 

 convolutions of a single tube ; in the more complicated pronephridia, 

 however, this canal may give off branches. It is to Goette and Furbringer 

 that we owe the first accurate account of the process of convolution. 



According to these authors, the gland is composed of two portions : a 

 " dorsal part " (collecting trunk and nephrostomal canals), which alone 

 receives the nephrostomes, 1 and a "ventral part" (common trunk), which 

 serves as the efferent canal, and is in communication with the anterior 

 end of the segmental duct. Both ventral and dorsal parts undergo ex- 

 tensive convolutions, and give rise to blind diverticula. Subsequent 

 authors have in general confirmed Fiirbringer's account, but have added 

 no new matter to the description. Selenka ('82) describes and figures 

 an interesting condition of the pronephros in Hylodes. The glands of 

 the two sides are unsymmetrical, and depart widely from the typical 

 structure known in Amphibia. Following the nomenclature which I 

 have proposed in the descriptive part of this paper, it is evident that the 

 nephrostomal canals and the collecting trunk are present, but do not 

 show the convolutions customary in these parts. The "ventral part" of 

 the gland, however, is not formed by the windings of the common trunk, 

 but is composed of great irregular blind pouches which communicate 

 with the collecting trunk, while the latter opens directly into the an- 

 terior end of the segmental duct. This condition of the pronephros evi- 

 dently represents the degeneration of the gland, and Selenka is inclined 

 to correlate the premature appearance of this complication in Hylodes 

 with the absence of gills in the larvae of this form. 



Kellogg has studied the structure of the pronephros in Amblystoma 

 and Rana by means of reconstruction from cross sections. His pre- 



1 Duval ('82, Fig. 7), figures the second pronephric nephrostome in Rana as open- 

 ing directly into the ventral part of the gland. I have never seen such a condition 

 in my preparations, nor do I know of similar observations being elsewhere recorded. 

 It seems likely that Duval has here fallen into error. 



