The developmeut of the iiriiiogenital organs of the lamprey. 29 



activity. The changes which the organ has undergone are considerable 

 but they are readily traceable to earlier conditions already described. 

 In Fig. 48 I have combined two sections separated by a considerable 

 si)ace, the one comprising only the glomus {pron.gl) and its artery 

 {gl. a), the other the remaining details shown in the figure. It will 

 be seen that the proiiei)hric lobe has increased considerably in size, 

 mainly through a distention of the cardinal vein, which is filled with 

 blood (bl) and envelops the pronephric tubules. These tubules, which 

 are cut at various points, are, of course, everywhere invested with 

 the flattened endothelium of the blood-vessel, so that they are, morpho- 

 logically speaking, really outside of the vessel, although they seem to 

 lie within its lumen. One of the funnels (pron.f), cut longitudinally, 

 is seen projecting horizontally into the pericardial cavity, with its 

 nephrostorae directed away from the glomus. The glomus itself is 

 more globular than in preceding stages and the pedicel through which 

 it receives the artery from the aorta is much narrower and farther 

 from the base of the pronephros. Comparison with Fig. 44 shows 

 that the capillaries in the glomus have grown smaller and more 

 numerous. 



Two matters connected with the pronephros require special con- 

 sideration, first, the orientation of the funnels which i)roject and oi)en 

 into the pericardial cavity, and second, the minute structure of the 

 pronephric tubules, funnels and duct. In the embryo there is a definite 

 and regular arrangement of the funnels, for with the exception of the 

 first, which atrophies, they all point directly downwards. In the Anmio- 

 cœtes from 8 mm in length on, this arrangement no longer obtains; 

 the funnels turn so that they lie in a horizontal position. The direction 

 of the uephrostomes varies, not only in the two pronephroi of the same 

 animal but also in the same pronephros. Thus in the Ammocœtes 

 9,5 cm long, the left pronephros had its first and second funnels 

 directed laterally, the third was directed dorsally on the inner side of 

 the pronephric lobe, so that it opened into the space between the 

 glomus and the intestine, and the fourth was directed backwards. 

 On the right side the first funnel was directed mesially, whereas the 

 second, third and fourth were all directed forward and formed a regular 

 overlapping series so that they were all included in a single sagittal 

 section. I have seen similar variations in the orientation of the 

 funnels in other larvie, so that I believe them to be normal and to 

 be, perhaps, an adaptation to favor a rather uniform absorption of 

 the pericardial fluid by the embryonic kidney. The funnels are so 



