The First Foundation of the Lnng of Ceratodus. 321 



A second stage is found in a specimen of three weeks, and 

 about 13 mm. in length. It shows the same pit in the mid- 

 ventral line of the pharynx, but the depression is deeper, 

 passes a little towards the posterior, and bulges somewhat 

 below the gut and at its side. The gut, which runs straight 

 back to the point of communication with the foundation of 

 the lung, here makes a rather sudden bend, so that the slight 

 backward prolongation of the tubular foundation (seen in 

 some fifteen sections, each about 10 /x thick) comes to lie at 

 the side of the gut, near its dorsal surface. (See Fig. 2.) 



A third stage is seen in 

 a second specimen of two 

 months and 15 mm. in 

 length. In this the found- 

 ation of the lung is still 

 in communication with the 

 mid-ventral line of the gut 

 (Fig. 3). It spreads out pri 

 below the gut, which it 

 almost equals in breadth, 

 and it gradually comes to 

 lie, first, laterally to it, and 

 at its posterior end dorsally. 

 In this specimen the whole 

 foundation extends to about 

 0-8 mm. 



Fig. 3. Letters as in previous figures. 



XXIV. Embryonic Excretory Organs of Ceratodus. (Prelim- 

 inary Notice.) By Gregg Wilson, Ph.D., D.Sc. 



(Read 21st March 1900.) 



The fore-kidney, or pronephros of Ceratodus, is distinctly 

 of the type found in Amphibia, and quite unlike what is 

 found in the Teleostomi. In the latter group there are 

 pronephric chambers, developed as diverticula of the 

 pronephric tubules, and in connection with these chambers 

 the "glomeruli" appear, projecting iuto the cavities. In 

 Amphibia, on the other hand, the " pronephric chamber " is 



