232 T. H. BuRLEND, 
There is no sign of a pronephric duct in this embryo. It will 
be noticed that the pronephros is confined to segments VII, VIII 
and IX on the left side, and to segments VII, VIIL IX and X on 
the right side. 
Plate 18, 19, Figs. 2 to 18 are photographs of sections 1,152 
to 2,7 of this embryo; they extend over practically the whole length 
of the pronephric region, at least on the embryo’s left side. 
It has been stated that in these early Selachian embryos the 
protovertebra, nephrotome, and lateral plate regions of the mesoderm 
are as yet undifferentiated, and so the particular region which gives 
rise to the pronephric rudiment in Selachii is not clear. This is 
certainly not the case in Scyllium canicula, for the lateral plate 
region of the mesoderm is never segmented, whereas of the seg- 
mented portions, the nephrotome region is readily distinguishable 
on account of the fact that the nephrocoel is a much larger space 
than the myocoel above it. 
Embryo C. 
3'/,—4 mm long. 26 protovertebrae. Six slides used in mounting, 
having respectively 97, 96, 97, 119, x, x, sections. 
Left side Right side 
2,26—2,53 Ear 2,34—2,61 
2,63— 3,4 I 2,68—3,2 
3,4— 3,22 EF 3,2—3,25 
3,22 —3,46 III 3,25—3,45 | 
3,46—3,64 IV 3,45—3,63 
3,64—3,81 V 3,63 — 3,83 
3,81—4,1 VI 3,83 - 4,4 
4,1—4,18 VII 4,4—4,921 
4,18—4,35 VII 4,21—4,37 
4,35 —4,49 IX 4,37— 4,53 
4,49—4.,65 x 4,53—4,67 
(This series of sections was cut much thinner than the others.) 
The primitive kidney groove is present on the left side from 4,1 
to 4,60, viz. in segments VII, VIII, IX and X: on the right side 
the groove is present from 4,4 to 4,62, viz. in segments VII, VIII, 
IX and X also. The pronephric duct is not yet present. The blood- 
vessels are not yet formed. Segmentalbläschen in segments II?, 
III---XIII?. 
