Goo. C. Price 



i;35 



oiHMi iul)u!(\'^ coiiu' to lie v(Mitral to the closed tubules, and also slightly 

 more lateral, and a transverse section may show parts of one or even of 

 two closed tubides, and at the same time parts of several open tubules. 

 Fig. 29 represents such a section. 'J'he pronephros now forms a promi- 

 nent body projecting into the crelom. The segmental duct is cut through 

 its posterior bend, and four open tubules are seen to be in connection 

 with it. By running along the series the lumen of these may all be 

 traced to a eoniuM'liou widi the duct on the one hand and with the 

 coelom on the ofhei'. Above, one of the closed tubules is cut through its 

 full length, but tlic lumen appears only at the point where it joins the 

 duct. Farther on in the series it niav be ti-aeed to a connection with the 





M.G 



Fig. us. 



Fig. 29. 



Fig. 28. — Sagittal section showing parts of seven tubules, and illustrating the way 

 in which they become crowded together. In studying the series all the tubules are found 

 to open to the cujlom. cm, coelom ; hv, blood-vessels ; d, segmental duct ; t, tubules. 



Fig. 29.- — Section of a pronephros showing the two kinds of tubules, four open tubules 

 below and a closed tubule above, cnic, cavity of the Malplghian corpuscle ; d, seg- 

 mental duct, here shown in two places ; yl, glomerulus of the closed tiihule ; t, tubule. 



cavity of the jMalpighian corpuscle. There are places in tlie pronephros 

 where the segmental duct has no lumen. This is the first embryo in 

 which the segmental duct was observed to open to the exterior at its 

 posterior end. 



In an embryo slightly older than the last, the pronephros was not 

 thoroughly studied, but it was observed to be more sharply set off from 

 the mesonephros than in the last, although the segmental duct was still 

 continuous between them. It occupied parts of the thirty- third and 

 thirty-fourth segments. The number of closed tubules was not deter- 

 mined, but two glomeruli were seen to be in very close contact with each 

 other. 



The next embryo is somewhat younger than embryo C of the previous 



