83 
remains of the larval pronephros. This identification is 
confirmed by a study of various early stages. In the 
youngest forms examined (symmetrical larve one to two 
weeks hatched), the mesonephric tubules are absent, or are 
only just forming, while the segmental duct extends 
anteriorly as a straight line which becomes convoluted in 
its anterior extremity forming the pronephros. In a later 
stage (asymmetrical fish 3/5th inch long) the three regions 
of the kidney described above are well marked, the latter 
portion presenting all the characters of a mesonephros, 
while the nephrostomes and glomi of the pronephros are 
still recognisable, though much reduced. In an asym- 
metrical form about one inch in length, the intermediate 
lymphatic portion is relatively shorter, the mesonephric 
portion with its Malpighian corpuscles has extended fur- 
ther forward, the pronephric convolutions of the seg- 
mental duct are still present, but glomi, pronephric 
chambers and nephrostomes have disappeared and lym- 
phatic tissue and blood spaces are largely developed. 
Finally in the oldest adult specimens examined the head 
kidney contains only lymphatic tissue. 
The pronephros probably degenerates in all Teleostean 
fishes with the exception of one or two specialised forms. 
Organs formerly supposed to represent a persisting func- 
tional pronephros such as are present in Lophius have 
been shewn to be anterior extensions of the mesonephros, 
and others such as those present in Anguilla and Hsow are 
lymphatic organs with degenerate remains of the 
pronephric convolutions. Only in Fverasfer, and perhaps 
Zoarces, is the evidence conclusive that a functional 
pronephros exists in adult life. In Dactylopterus Calder- 
wood* has described an organ which he regards as a func- 
tional pronephros, but in this case it is still probable that 
* Jour. Mar. Biol. Assoc., vol. ii. (N. S.), pp. 43-46, 1891-2. 
