208 G. C. PRICE, 



open into the pericardial cavity. At the posterior end there is a large 

 glomerulus. In some of his specimens, though not in all, Weldon 

 found traces of the continuation of the segmental duct into the head 

 kidney, although in no case did he find a continuous lumen in the 

 connecting piece. I can not say whether any such rudiment exists in 

 the California species or not, but we shall learn later on, that in the 

 embryos there is a connecting portion of the segmental duct, which, 

 later degenerates. In some cases the atrophy might be complete, and 

 in others only partial. It is certain that here as in Bdellostoma 

 forsteri the lumen of the central duct of the pronephros is not con- 

 tinuous with the lumen of the segmental duct, and that therefore the 

 pronephros cannot be functional as an excretory organ. 



In the Myxinoids there is no connection between the reproductive 

 and the excretory organs. 



In the preliminary papers above referred to, the three embryonic 

 stages are designated as A, B and C. Of these A and B are com- 

 paratively early stages, and do not differ widely in point of develop- 

 ment from each other, while C is much further advanced, and in many 

 points resembles the adult. 



In order to give a general idea of the excretory system in the 

 younger embryos, it may be said that it here extends through the 

 body from the sixth to the eightieth spinal ganglion, and consists of 

 a series of short, segmentally- arranged tubules, which occur in all the 

 segments except the last two, and which open from the body-cavity 

 on the one hand, and into a segmental duct on the other. The above 

 statement is not strictly true for the system at any one time, for by 

 the time the anterior part, which develops most slowly, has reached 

 the above described condition , some of the tubules in the posterior 

 part have degenerated, and others have lost their connection with the 

 body-cavity. Then too the segmental duct is in many places not a 

 tube, but a solid rod of cells. The strict segmental symmetry may 

 be slightly disturbed by the interval between two tubules being now 

 a little greater, now a little less. This is especially true for the an- 

 terior end, which early degenerates, and here the number of tubules 

 may even slightly exceed the number of segments. 



Passing now to a more exact description of the system in the 

 three stages, it will be well at first to glance at a transverse section 

 through the body of an embryo of stage A (Fig. 1), in order to see 

 the relation of the excretory organs to other parts of the body. The 



