Geo. C. Price 137 



pericardial cavity, in a position corresponding to that of the adult. 

 There are on the left side twenty tubules, two of which can be traced to 

 a glomerulus and must therefore represent closed tubules. Some three 

 or four of the open tubules have begun to branch, as is shown in the 

 one in Fig. 31. This is the beginning of a process which results in 

 the formation of the scores of pronephric funnels found in the adult. 

 The two closed tubules are small and insignificant, but the glomerulus 

 to which they go is large and well defined, and has something the 

 appearance of having been formed by the fusion of two glomeruli. At 

 one point, shown in Fig. 31, the cavity at the side of the glomerulus, 

 the cavity of the Malpighian corpuscle, is almost in communication with 

 the coelom. This is interesting as suggesting that in some cases the 

 communication might actually occur, in which case the glomerulus would 

 be virtually in the body-cavity. However, this is to be regarded as only 

 a passing remark, and not as suggesting a homology between this glomer- 

 ulus and the glomus of the pronephros in other forms. ISTothing of 

 the kind occurs on the other side, nor has it been observed in any other 

 embryo. There is a complete break in the segmental duct between the 

 pronephros and mesonephros. In the pronephros itself the duct is dis- 

 tinct and the lumen well defined through about half its course on one 

 side and two-thirds on the other. In the rest it is solid, and in places 

 quite small. It may be remarked that no case has yet been observed 

 where the lumen of the duct is continuous throughout tlie entire pro- 

 nephros. 



A point that has not been worked out is the manner in which tlie 

 segmental duct becomes shortened as the tubules are crowded together. 

 The bending of tlie duct previously described accounts for part of it 

 though hardly for all. 



The account of the pronephros just given does hot fit in well with 

 Mass' ' description of this organ in a 3'oung specimen of IVIyxine. wliei'o 

 there is no segmental duct; but the difference is hardly to be accounted 

 for on the supposition of errors of observation in either the one case or 

 the other, nor is it likely that later the pronephros of Bdellostoma would 

 come to be more like that of the young Myxine. An examination of the 

 pronephros of the adult Bdellostoma reveals the presence of a true 

 segmental duct, although it may not be continuous through the entire 

 organ, while, judging from the published accounts of the pronephros of 

 Myxine, the presence of a true segmental duct here would seem to be 

 very doubtful. In the light of iJiis the above discrepancy is not sur- 

 prising. 



'Mass, Otto: 1. c. 



