212 G. C. PRICE, 



We now come to speak of the relation of the tubules to the 

 coelom, and it will first be asked, are the tubules formed from the 

 lower portion of the primitive segments, that is from nephrotomes? 

 This question can not be satisfactorily answered, for even in the 

 youngest embryo the myotomes are entirely separated from the un- 

 segmented portion of the coelom, and throughout the greater part of 

 the system the tubules are already formed. In the anterior region, 

 where the tubules are just forming, they come undoubtedly as evagin- 

 ations from the body-cavity. But here the system is rudimentary, 

 and it will not do to argue that the earlier formed tubules must also 

 have come from the same part of the coelom. We can only say, 

 therefore, that the material in hand gives no indications that the 

 tubules are formed as evaginations from nephrotomes but the question 

 can be satisfactorily answered only by the study of younger material. 



In the anterior part of the system, as can be seen from Figs. 2, 

 3, 4 and 5, the anlages of both duct and tubules lie some distance 

 lateralwards from the inner angle of the body- cavity. In the region 

 of the twenty-first segment, that is , ten segments caudalwards from 

 the anterior end of the system, the beginning of a process is met 

 with which changes the relations of these parts, and at the same time 

 results in the formation of certain coelomic pockets, which stand in 

 intimate relation with the tubules. 



The first step in this process is illustrated by Figs. 9 a — 9f, a 

 series taken from a somewhat younger embryo than the one hitherto 

 spoken of. Here, midway between two tubules, the somatic and 

 splanchnic layers of the coelomic epithelium have met and fused with 

 each other in such a way as to cause the inner angle of the body- 

 cavity to lie more lateralwards, and to come to lie directly under the 

 segmental duct (Fig. 9 a). In the next section (Fig. 9 b) the fusion 

 has not been carried so far, and in the four following sections, in- 

 cluding the two (Figs. 9e and 9f) in which the tubule evagination 

 occurs, no indication of fusion is seen. Midway between this tubule 

 and the following one, a fusion similar to that illustrated in Figs. 9 a 

 and 9 b has taken place, and as a result, a wide and shallow pocket 

 is formed, from the dorsal side of which the tubule evagination pro- 

 jects. Measurements show that the segmental duct lies parallel with 

 the notochord, so that the appearance here described can not be the 

 result of a bend in the duct. Still caudalwards the process has been 

 carried further, so that here the duct does not lie over the inner 

 angle of the body-cavity, but a little distance medianwards. At the 



