206 G. C. PRICE, 



96^), sorae of the more important results obtained from a study of 

 these embryos have already been given. 



In my material only three embryological stages are represented, 

 and naturally it has neither been possible to obtain a complete history 

 of the development of the animal as a whole, nor of the development 

 of any one system of organs. This remark applies with much less 

 force, however, to the excretory system than to any other. This is 

 owing partly to its simplicity, and partly to the fact that it does not 

 develop with equal rapidity in all portions of its length, so that in 

 one embryo diöerent stages in its development are represented. In 

 the present paper a somewhat detailed account of the development 

 of this system will be given. 



It would perhaps be more logical to give first a description, with 

 figures, of the entire embryos, together with an account of the egg- 

 laying habits so far as known, and the manner of obtaining the ma- 

 terial. The reason for not following this course is that there is a 

 possibility, perhaps only a remote possibility, of finding more material 

 awaiting me on my return to California, and in such case a more 

 satisfactory account could be given than would be possible at present. 

 But if disappointed in obtaining additional material, I shall never- 

 theless publish, as soon as possible, a full account of the facts now 

 in my possession, unsatisfactory and fragmentary as such an account 

 must necessarily be. 



Before* proceeding to an account of the development of the ex- 

 cretory system, it will perhaps be well to say a few words in regard 

 to its structure in the adult. 



The system here consists of two parts, which are described by 

 the authors as pronephros or head kidney, and mesonephros or 

 Wolffian body. 



The mesonephros, which is alone functional as an excretory organ, 

 begins on each side just back of the pericardial cavity, and extends 

 caudalwards to a point a short distance back of the posterior end of 

 the body-cavity. It is remarkably simple in its structure, consisting 

 of a relatively large segmental duct, into which empty, along the 

 median side, short, segmentally arranged tubules. Anteriorly the duct 

 begins blindly, posteriorly the ducts from the two sides bend slightly 

 ventralwards, and, converging towards the median line, open beside 

 each other into the urogenital sinus. In five specimens of the Cali- 

 fornia species which were examined, the number of tubules varied from 

 twenty-six to thirty-one, and occurred along the anterior two thirds 



