DEVELOPMENT OF THE FAT-BODIES IN EANA TEMPORARIA. 129 



The fate of the pronephros in the frog, as above described, throws 

 some light on the condition that obtains in other groups of Verte- 

 brates. 



It was stated by Balfour* that " the pronephros atrophies more or 

 less completely in most types, though it probably persists for life in 

 the Teleostei and Ganoids." 



In a later paper,! however, after working over the condition of the 

 kidneys in the sturgeon and in certain Teleostei, he stated that " the 

 whole of the apparent kidney in front of the ureter, including the 

 whole of the so-called head kidney, is simply a great mass of lym- 

 phatic tissue, and does not contain a single uriniferous tubule or 

 Malpighian body," from which he concluded that both in Ganoids 

 and in Teleostei the organ usually held to be pronephros is actually 

 nothing of the kind. He therefore considered that Rosenberg; was 

 mistaken in thinking that he had traced in the pike the larval organ 

 into the adult part of the kidney called by Hyrtl the pronephros ; 

 and his final conclusion was " that the pronephros, though found in 

 the larvae or embryos of almost all the Ichthyopsida, except the 

 Elasmobranchii, is always a purely larval organ, which never con- 

 stitutes an active part of the excretory system in the adult state." 

 But Balfour did not apparently regard it as possible that the prone- 

 phros might continue in the Ichthyopsida in a modified condition, 

 but thought that if it did not persist with at least its original 

 structure, if not its original function, it must have disappeared 

 altogether. He was, however, led to this conclusion by the study 

 not of their development, but of their adult structure. 



But it seems to me, from a consideration of the state of things in 

 the tadpole and young frog as above described, that it is not at all 

 necessary that the pronephros, if it persist, should retain its original 

 structure any more than its original function ; that it is quite 

 possible that Rosenberg's observations were correct, since the only 

 argument adduced against them is this alteration of structure, and 

 that there is nothing in Balfour's observations on the Ganoids and 



* " Comparative Embryology," vol. ii., p. 729. 



t " On the Nature of the Organ in Adult Teleosteans and Ganoids which is usually 

 regarded as the Pronephros or Head Kidney," "Quart. Journ. Micr. Sci.," vol. xxii., 

 N.S., 1882. 



J " I'ntersuchungen Liber die Entwieklung der Telrostierniere," Dorpat, 18G7. 

 K 



