384 s. HATTA : 



somite develops solely into the tubule, and by tlie secondary 

 union of the tubules' ends, the collecting duct is brought about. 



As regards the number of the tubules, tliere are, in 

 Pelromyzon, only two pairs in the branchial region instead of 

 twenty in Bdrllxtoma. The number is, however, of secondary 

 importance ; it varies with the stages of embryos and possibly 

 with individuals, and naturally more with tlie embryos of 

 different families. This nuuierical variation is readiW explained 

 by the degenerating tendency of the tubules. 



Price has made out the segmental evaginations of the dorsal 

 corner of the coelomie cavity corresponding to the nephromeres ; 

 they are called by him the " coelomie pockets." In Fetromyzon, 

 I have found a series of solid knobs on the visceral layer of 

 the intermediate cell-mass, which are transformed into the 

 segmental folds of epithelium, forming then the direct continua- 

 tion of the peritoneum. Thus the coelomie pocket in Bdellostoma 

 and the coelomie projection in Petromyzon are apparently very 

 similar structures; the two, however, differ from each other in origin 

 and in fate. The former (coelomie pocket) is constructed by the 

 parietal and visceral layei's of the lateral plate, while the latter 

 (coelomie projection) is the product of only the visceral layer 

 of the nephrotorae, the ventral half of the segmented part of the 

 mesoblast. The coelomie pockets become the Malpighian body, 

 and the coelomie projections give origin to the radix of the 

 mesentery, from which the gonad-cells and the mesouephric 

 tubules are derived. Nevertheless, these two structures are, I 

 believe, homologous. Price's statements on the derivation of the 

 coelomie pocket from the two peritoneal layers, are not as clear as 

 is desirable, and its partition fiom the body-cavity might, it 

 seems to me, represent the uppermost peiitoneal partition which 



