12 
iVlONICA TAYLOR. 
evidently a striking object in tlie living larva. The sections 
show that the blood-vessels of the fins are well established, 
the arterial supply being derived from the dorsal aorta in the 
neighbourhood of the pronephros immediately behind the 
heart, the venous blood being returned to the duct of Cuvier. 
In Symbranchus it is impossible to say dogmatically that 
the artery to the pectoral fin has been derived from an inter- 
segmental artery (i. e. is a primary subclavian artery^) because 
of the precocious development of the fin in question, but a 
comparison of the early development of the fin artery with 
the intersegmental arteries (PI. 4, fig. 27) that arise later on 
when the myotomes are fully formed shows that the arterial 
supply to the fins is intersegmental in nature. Three 
myotomes take part in the formation of the fin ; whether the 
subclavian in Symbranchus represents the intersegmental 
ai'tery of one or the fused intersegmental arteries of all three 
myotomes it is not possible to say. 
Stage 29. — There is a shrinking in the rostrum at this 
stage. From now onwards this structure gradually diminishes 
in size. Chromatophores appear, being confined to the head 
at first. On the right-hand side of the creature the ccelom is 
visible externally, the liver being conspicuous on the left. 
In Stage 29 the inclusion of the yolk in the abdominal 
cavity commences. This has an important effect on the 
contour of the creature, as may be seen by comparing PI. 1, 
fig. 9, and PI. 2, fig. 13. 
Stage 30,^ (Pi. 1, fig. 10). — The creature at this stage is 
13 or 14 mm. in length, its rostrum being 1 mm. long. There 
has been a great forward growth of head, which is assuming 
a definitive form, the optic lobes are covered with a pigmented 
epithelium, cranial flexure has almost disappeared. The eyes 
are fully developed, and in contrast to later stages are only 
just visible in dorsal view. 
^ Hochstetter in Hertwig, O., ‘ Hanclbucli der vergleiclieiideii mid 
experimentelleii Entwickeiungslehre der Wirbeltiere.’ 
- In writing the descrix>tion of this stage I have been aided by a large 
drawing made by Dr. Agar from the living larva. 
