NOTES ON ELASMOBRANCH DEVELOPMENT. 585 
EXPLANATION OF PLATE XXXV, 
Illustrating Mr. Sedgwick’s ‘‘ Notes on Elasmobranch 
Development.” 
Fie. 1.—Embryo of Scyllium canicula, 24 mm. in length. The hinder 
end of the embryo is notched. The medullary groove is just beginning. The 
tail swellings of Balfour are well marked. 
Fic. 2.—Embryo of Raja ? sp., 4 mm. in length. The medullary groove is 
closed except at the hind end. The notched embryonic part of the edge of 
the blastoderm has grown faster than the rest, and come to project over the 
surface of the yolk. The sides of this projection are already slightly bent 
ventralwards. They will eventually meet and form the ventral part of the 
caudal region of the body. 
Fic. 3.—Raja ? sp. Embryo of Stage E or F, 44—5 mm. in length. The 
medullary canal is still open, but the medullary folds are almost touching 
except behind, where the medullary canal widens out in a wide medullary 
groove, in the floor of which is placed the dorsal part of the blastopore. The 
blastopore is slit-like, but dilated in front; posteriorly it is continued round 
the hind end of the body into the ventral portion. 
Fic. 4.—Raja ? sp. Stage H or F, 5—54 mm, in length, a little older than 
Fig. 3. Medullary canal closed except behind, where it widens out and 
encloses the blastopore. The blastopore is slit-like, but the hinder end of 
the dorsal portion is faintly marked. 
Figs. 8 and 4 are somewhat diagrammatic, but they show correctly the 
relations of the medullary groove and dorsal part of the blastopore. I 
hope to publish figures of the sections through them shortly. 
Fie. 5.—Ventral view of head of Scyllium canicula between Stage I 
and K. Total length 7—8 mm. The two first pharyngeal clefts are open. 
The mouth rudiment is present as a longitudinal groove in the ectoderm of 
the buccal depression, which is fused with the endoderm. At intervals there 
are perforations along this groove. The groove reaches into the rudiment of 
the pituitary body. The mandibular arch is present as a backwardly directed 
longitudinal ridge, and bounds the buccal depression externally. 
Fic. 6.—Ventral view of head of Scyllium canicula a little older than 
the preceding. The buccal groove has become a longitudinal slit. 
Fic. 7.—Side view of head of Scyllium canicula a little younger than 
Stage K. Total length about 9mm. I could not distinguish any trace of 
VOL. XXXIII, PART IV.—NEW SER. RR 
