Tlie development of the urinngenital organs of the lamprey. 97 



sagittal plane of the embryo so that it may be easily -traced in a 

 few consecutive sections. In stage 9, which corresponds with Goette's 

 Fig. 12, a stage in which the lumen of the intestine temporarily dis- 

 appears, the contortion of the collecting duct immediately behind the 

 pronephros and dorsal to the liver becomes more excessive. 



In this stage, also, the glomus is somewhat lobular. In sagittal 

 sections four or live lobes may be distinguished. It is possible to 

 trace the same conditions in some specimens as early as stage 4. 

 The number of vessels that sui)ply the glomus is not, however, so 

 easily determined. In one embryo in stage 6 I can detect distinct in- 

 dications of four diverticula from the aorta on either side extending 

 down into the glomus. In stage 9, where the conditions are very 

 clear in well preserved embryos, I find only three such vessels on 

 either side, or two on one side and three on the other. The section 

 represented in Fig. 44 passes through one of these arteries (gla) filled 

 with blood corpuscles which have entered it from the aorta (ao). This 

 segment also shows that pigment is being deposited in the walls of 

 the arteries and cardinal veins and between the loops of the pro- 

 nephros. There is also some similar pigment l)etween the neural tube 

 and the myotonies. In the proiiephric funnel cut at pron.f the cilia 

 are already formed and directed up into the lumen of the tubule. 

 The origin of these cilia may be dimly traced in this and the pre- 

 ceding stage (8). They are at first very short, hyaline prolongations, 

 one from the free surface of each cell in the wall of the nephrostome. 



Stages 10 and 11 are characterized by the appeal ance of the 

 spiral valve of the intestine. This is before the yolk has completely 

 disappeared from the entoderm cells, which are about one third the 

 diameter of the intestine including the breadth of its lumen. In 

 stage 10 the spiral valve is only feebly indicated in the mid-dorsal 

 line of the intestine ; in stage 11 it is more distinct and has moved 

 a little to one side owing to the peculiar intestinal rotation described 

 by GoETTE (1<S90). In these stages each glomus is supplied by only 

 a single artery. The mesenteric artery to the spiral valve leaves the 

 aorta a short distance behiod the vessels to the glorai. Each cardinal 

 vein sends hollow and anastomosing branches into the spaces between the 

 loops of the pronephros of its side, so that later the pronephros is really 

 embedded in the cardinal vein. The vein and pronephros thus acquire 

 the same relations to each other that the vitelline veins bear to the 

 liver in the higher Vertebrates. The small vascular sinuses at the 

 termination of the artery in the glomus obviously communicate with 



