The pronephros of Scyllium canicula. 239 
2, 18—2,98 IV 2,17—2,28 
2,28 —2,38 Vv 2,27—2,39 
2,38—2,48 VI 2,392.48 
2,482.58 VII 2.49 2.58 
2,57 — 2,67 VIII 2,59 —9,71 
2,68—2,76 IX 2,72—2,82 
2,77 2,84 x 2,82 — 
The first, second, third, and fourth gill-pouches are open to the 
exterior: the fifth pouch on each side is present, but still closed. 
On the left side the pronephros is visible as an open groove 
from 2,51 to 2,62. After this section the duct is closed off from the 
mesoderm, but has a solid connection with it as far back as 2,65. 
In 2,66 the duct is open to the coelom. In and behind 2,68 the 
duct has no connection with the coelom. There are no remains of 
arteries on this side. Thus there are two pronephric nephrostomes 
on this side, the first extending over the posterior part of VII, and 
the front part of VIII, whilst the second occupies a position in the 
posterior region of segment VIII. 
On the right side the pronephros is present as a groove from 
2,51—2,59; shut off from the coelom but having a solid connection 
with it in 2,60, 2,61 and probably 2,62. There is a nephrotomie 
opening in 2,63, and a coelomic opening in 2,67 and in 2,68, but in 
the intervening sections only a solid connection between duct and 
coelom exists. 
After 2,68 the duct is not connected with the coelom. 
Hence we have on the right side at this stage: 
first nephrostome — greater part of VII and anterior part of VIII 
second nephrostome — middle of VIII (opens into nephrotome), 
third nephrostome — posterior end of VIII. 
The vitelline artery in this Embryo can be seen in the series 
of sections shown on Plates 24 to 25 (Figs. 75 to 85). 
Embryo J. 
7!/, mm long. Fixed in sublimate acetic. Stained with DELAFIELD’s 
Haematoxylin, and Eosin in abs. alcohol. Mounted the sections upon 
8 slides, having respectively 59, 56, 56, 59, 53, 48, 52 and 48 sections. 
About 70 protovertebrae present. 
