586 ADAM SEDGWICK. 
the limbs. I do not think the fourth slit is open. The posterior end of the 
mandibular arch is slightly bent ventralwards. 
Fic. 8.—Ventral view of head of same embryo drawn to a slightly smaller 
scale. The anterior part of the buccal slit has become much wider. 
Fie. 9.—Side view of head of Scyllium canicula about Balfour’s 
Stage K. Total length about 11—12 mm. External gills have appeared 
on the first and second branchial arches. The ventral bend of the hind end 
of the mandibular arch is more marked. 
Fic. 10.—Ventral view of the same head drawn to a slightly smaller scale. 
The future angle of the jaw can be distinguished, the mouth being widest at 
that point. The posterior slit-like part of the mouth is still present. 
Fic. 11.—Side view of head of Scyllium canicula about Balfour’s Stage 
L. Total length about 16 mm. The external gills have increased in number, 
and are present on the mandibular arch. The angle of the jaw where the 
lower part of tle mandibular arch bends ventralwards is very marked. 
Fic. 12.—Ventral view of same head drawn to a smaller scale. The mouth 
has much widened, and the posterior slit-like part has almost. entirely dis- 
appeared. The anterior part of the mandibular arch has a process towards 
the middle line. The hinder end of the body has been tilted upwards so as to 
bring the fronto-nasal process into view. 
