Lilian V. Sampson 495 



section the tubules appear to be, through several stages including Sel- 

 enka's early stage, as regular as in sections of Eana. It would be of inter- 

 est to determine the exact state of the organ from a series of models; 

 but at present, I can only give a brief statement of the time of appear- 

 ance and duration of the principal parts of the excretory system. 



The Wolffian ducts are found in stage II. While the archenteric 

 cavity is still broad, their posterior ends are far apart, but when the gut 

 has been differentiated from the archenteron, they meet in the median 

 line, where they open into the gut. It has already been noted that from 

 this point backward, the gut remains open as the cloaca. It seems to be 

 the enlargement of the gut which Selenka calls the " allantois." 



The tubules of the pronephros are already present in stage III in a 

 simple form; in IV, they are much coiled, and before stage VI they 

 form a compact organ. In stage III, the three ciliated funnels open into 

 the peritoneal cavity (cf. Figs. G2, HI, 2, ne), the two anterior funnels 

 close together. In XI, the tubules of the head-kidney are irregularly 

 dilated; in XIII, the organ is reduced in size, and the tubules are solid 

 in part. Vestiges of the ciliated funnels persist until XIV, when their 

 number cannot be determined from the sections. In XV, the degenerate 

 pronephros has almost entirely disappeared. The Wolffian duct remains 

 connected with the head-kidney until stage XV, when only a vestige of 

 it remains anterior to the Wolffian body. The glomus is present in stage 

 IV (Figs. Gl, 2, gl), and develops and degenerates at a nearly equal 

 rate with the pronephros, except in later stages, when it is particu- 

 larly large relatively to the size of the head-kidney. In stage XV a 

 vestige of it still persists. 



About four or more mesonephric tubules are present in stage VI, and 

 from that time they increase in number, size and complexity until they 

 have become a compact mass (stage XV, cf. Figs. M, 0, k). 



The bladder appears at about stage X as a solid projection of the 

 ventral wall of the cloaca. As it develops, it extends anteriorly, becomes 

 hollow and distally bifid (from stage XI), and by stage XIV, it is a 

 thin-walled cleft sac of considerable size (cf. Fig. 0, b). 



The genital ridges arise at about stage VII, and are well developed in 

 stage XV (cf. Fig. M, r). At that time, there is no appearance of 

 degeneration of the anterior portion into fat bodies, no differentiation 

 into testes or ovaries, nor has the rudiment of the Miillerian duct been 

 seen. 



5. TAIL. 



The tail of Hylodes calls for particular attention because of the unusual 

 condition of almost every feature of it. In a word, it constitutes not a 

 muscular organ for locomotion but a vascular organ for breathing. 



