Goo. C. Price 131 



pinched oil: from ilie (hiel nnd would soon entirely disiippear. As a rule 

 the degeneratiiii;- tubules do not beeome thus separated from the duct. 



In the earlier paper the -statement was made that the excretory system 

 developed from behind forward. This was based on two facts; first, 

 in passino; from the anterior end backward through a number ol' seg- 

 ments in both stages A and B, both the duct and tubules became gradually 

 better and better dilTerentiated ; and second, in the older embryo the 

 system extended a little farther forward than iu 11 le younger. From the 

 last it was assumed that if the younger embryo had developed the system 

 would have extended as far forward as in the older, but this does not 

 follow, as is proved by the examination of a larger number of embryos. 

 The above ojnnion was further strengthened by the observation that the 

 first tubules to be cut off from the connection with the splanchnocoel were 

 at the posterior end. From the material at hand it cannot be determined 

 which are the first neplirotomes to appear although it would seem that 

 those at the posterior end are the last. The formation of the excretory 

 system proper seems to begin in a good many segments at about the same 

 time, but the d(>velo]iinent lags heliind at the anterior end, and this gives 

 lise to the appearance in certain stages of this being the youngest part. 



The mistake of looking upon the anterior end as the youngest part 

 led to the more serious error of supposing the nephrotomes were pockets 

 formed from the unsegmented mesoblast; for at the anterior end where 

 the tubules were apparently just appearing there were no indications 

 of nephrotomes. the tubules being connected with the unsegmented body- 

 cavity. Then in passing back, as the tubules became better and better 

 developed they were connected at first with very shallow pockets and then 

 with deeper and deeper ones. We now know that this appearance is due 

 not to the formation of segmentally arranged pockets, but to the dis- 

 appearance of nephrococls. In a review Felix' pointed out the proba- 

 bility of this error. 



Til what was supposed to be the youngest part of the system the segmental 

 duct was found to be in connection with the coelomic epithelium. This 

 union is seeoiulary, but it was then thought to be primary, and it was 

 supposed that the duct in all parts arose as thickening of the ccelomic 

 epithelium. The theory was strengthened by finding the duct in con- 

 nection with the coelomic epithelium in one individual in some of the 



° Felix, W. : Die Price'sche Arbeit "Development of the excretory organs 

 of a Myxinoid (Bdellostoma stouti Lockington)" und ihre Bedeutuiig fiir die 

 Lehre von der Entwickelung des Harnsystems. Anat. Aw/.., Vol. 13, Nos. 21 

 and 22, 1897. 



