262 T. H. Buruenp, 
Fig. 42. A photograph of section 2,44 of embryo E. The section 
passes through the front end of proto. VII on each side. It exhibits 
very well on the right side the pronephrie rudiment arising as a groove 
of the somatic layer of the lateral plate. Compare with Fig. 20. 
Figs. 43—73 are photographs of successive sections through Embryo F; 
this series shows the whole of the pronephric region on the animals 
right side. 
Fig. 43 (Section 2,31). On the right side of the figure there is 
visible a swollen nephrocoel or “Segmentalbläschen” of van Wine. The 
pronephros does not begin until about four sections further back. 
Fig. 44 (Section 2,32). Notice the vascular projection from the wall 
of the gut on the left side of this and neighbouring sections; it is supplied 
by the right pronephric arteries. 
Fig. 45 (Section 2,33). It will be seen, on comparison of this 
section with those in front and behind, that the protovertebra is directed 
obliquely backwards, and so, although the section passes through the 
posterior region of the protovertebra dorsally, it passes through an inter- 
segmental region at the level of the nephrotome. 
Fig. 46 (Section 2,34). On the left side of this figure is shown the 
invagination of the splanchnic layer of the lateral plate mesoderm towards 
the aorta; presumably this invagination is related to the formation of 
pronephric arteries, since it is not so noticeable or perhaps absent on the 
other side of the figure. 
Fig. 47 (Section 2,35). Notice the presence of a blood-vessel, which 
produces a bulging out of the gut-wall into the coelom beneath the pro- 
nephros on the animal’s right side. This blood-vessel is in communication 
with the vitelline artery, and is probably of the nature of a “glomus” in 
this region of the body. ; 
Fig. 48 (Section 2,36). Shows a blood-vessel passing from the aorta 
to the right pronephros; the section is in the region between segments 
VI and VII on the right side of the body. 
Plate 22. 
Fig. 49 (Section 2,37). The aortic branch (between segments 
VI and VII on the embryo’s right side) is cut longitudinally in this 
section. This pronephric artery passes into the vascular out-growth on 
the gut-wall (glomus) in section 2,39, Fig. 51. 
Fig. 50 (Section 2,38). The left pronephros (anterior limit) is shown 
on the right side in this figure. 
Fig. 51 (Section 2,39). Notice the glomus on the animal’s right 
side only; its presence causes the splanchnic mesoderm in the lateral plate 
region to be pushed up towards the pronephros. 
