252 T. H. BURLEND, 
nephric arteries 2 and 3, whilst 1 and 4 may or may not take part, 
RÜCKERT and van Wine said that the arteries abort until one alone 
remains, and this becomes the vitelline artery. In Seyllium canicula 
it would appear that artery 1 usually persists and gives rise to the 
vitelline artery (see embryos I and J), although artery 2 may take 
part in its formation, at least for some time after 3 has disappeared. 
In most other respects my observations are in agreement with 
those of Rast, though I believe that the pronephric arteries are 
not segmental in position but are situated between the tubules. 
Moreover I have never found 4 nephrostomes on each side or 4 
pronephric arteries in Scyllium canicula. 
Left Right 
Left Right L 
Section 2.38 Left Right 
2.48 
243 a 
2.53 
47 
2.48 
2.58 5 
à ı one 3.52 
a YA 
à D 3.57 T 
Fig. A (EmbryoE). Fig. B (Embryo F). Fig. D (Embryo H). 
nephrostome Left Richt 
I 
4.32 ; neph. 
| 
4.371 
neph 5 
; 4426 de 
a : prea 
ry: 447 : 
$e: 3.79\ i 
Fig. E (Embryo I). Fig. F (Embryo J). Fig. G (Embryo K). 
NB. Although these diagrams are drawn to scale so as to give the pro- 
portions of blood-vessels, nephrostomes and ducts longitudinally, this does not 
apply to their transverse proportions. Thus the aorta would have to be represented 
as many times wider than the pronephric arteries, if it were drawn to scale. 
In order to verify my results on the condition of the pronephros 
and its blood-supply at different stages, I plotted out upon squared 
paper (one division to a section), the relative positions of arteries 
and nephrostomes, as soon as they could be recognized, of the pro- 
nephros of Scyllium, thus adopting the method employed by Rast. 
The Textfigures A to G illustrate the condition of the pronephric 
arteries and nephrostomes in embryos E—K. 
