240 
T. H. Burtenp, 
Left side Right side 
2,16— 2,37 Ear 2,17—2,37 
— 3,26 I — 3,27 
3,28—3,37 IT 3,31—3,39 
3,39—3,49 III 3,40—3,51 
3,50—4,6 IV 3,53 — 4,7 
4,7—4,16 V 4,8—4,19 
4,18—4,26 VI 4,21—4,28 
4,28—4,35 VII 4,30—4,37 
4,36 —4,43 VIII 4,39 —4,46 
4,45—4,52 IX 4,49 —4,55 
The first four gill-clefts on each side are open and the fifth is 
nearly open. 
On the left side the pronephros extends as an open groove from 
4,32 to 4,38. In sections 4,39, 4,40 and 4,41 the groove is practically 
closed off from the coelom, but has a solid connection with it. Again 
in the next two sections 4,42 and 4,43 the groove is open; in 4,44 
and all succeeding sections the duct is distinct from the mesoderm. 
The nephrostomes on this side are: 
first nephrostome opposite post. portion of VII 
and ant. portion of VIII 
second nephrostome opposite the post. end of VIII. 
On the right side there is an open pronephric groove of the 
coelomie wall from 4,32 to 4,39. This is almost closed in 4,40, and 
opens into the lower end of the nephrotome. The groove is closed 
in 4,41, open in 4,42, and again in 4,43. The groove is completely 
closed and not joined even by a solid connection with the coelom 
in and after 4,44. Hence there are the remains of two nephrostomes 
at this stage on the right side: 
first opening greater part of VII 
and ant. end of VIII 
second opening middle of VIII. 
There seems to be no trace of an aortic branch to the pronephros 
on the left side. On the right side the aorta bulges out at 4,28 
onwards to 4,34, where its wall fuses with that of the gut. From 
4,35 to 4,41 the aorta passes into a large vitelline artery. Behind 
4,42 the vitelline artery is not sectioned proximally. 
