210 G. C. PRICE, 



wards, it is found that between this and the anläge in the following 

 segment there are three sections in which there are no traces whatever 

 of the excretoiy system. 



In the segments immediately following, there are epithelial 

 thickenings somewhat similar to the one that has just been described, 

 but in each one the beginning of a segmental tubule is marked by a 

 slight, though unmistakable evagination. This is shown in Fig. 5, a 

 section through the fourth anläge from the anterior end, that is, the 

 one in the fourteenth segment. 



The evagination in the twelfth segment is connected with the 

 one in the thirteenth by a streak of columnar epithelium, which in 

 transverse section (Fig. 3) resembles the first tubule anläge (Fig. 2), 

 except that there is no concavity on the lower surface. This is the 

 anläge of the segmental duct. Between the evagination in the thirteenth 

 segment and the one in the fourteenth the anläge of the duct is more 

 than one cell thick (Fig. 4), and has somewhat the form of a low 

 ridge of cells. Between the evagination in the fourteenth segment and 

 the one in the fifteenth there is in two sections almost a complete 

 break in the continuity. 



The relations of the parts thus far described will be better under- 

 stood from the diagramatic longitudinal section (Fig. 6). The 

 Figs. 1 — 5 indicate the corresponding tubule anlages, and correspond 

 in position with the segments 11—15. Here the evaginations recur 

 in strict segmental order, but in the five following segments this order 

 is broken, there being seven instead of five evaginations. This is the 

 only case of such irregularity in this embryo. 



Following the series caudalwards the tubule evaginations gradually 

 become deeper, and the anläge of the segmental duct first forms a 

 more prominent ridge, and then becomes constricted off from the 

 coelomic epithelium, and forms a rod of cells. All this can be well 

 seen in Figs. 7 a — 7j, which represent a complete series through th& 

 eleventh and twelfth tubules , and the connecting portion of the seg- 

 mental duct. The tubule evaginations are still shallow (Fig. 7a and 7h), 

 although they are not much deeper in any part of the system. The 

 process of formation of the segmental duct is here well illustrated. 

 In three of the six sections (Figs. 7 b, 7 c and 7 g) which occur between 

 the two tubules the anläge of the duct forms a ridge, in two others 

 (Figs. 7 d and 7 f) it is partly constricted off from its connection with 

 the coelomic epithehum , while in still another (Fig. 7 e) the con- 

 striction is complete. In the section following the second tubule 



