LARVAL SHARKS 215 
cavity of the intestine, the only instance of this condition 
known among fishes (Ceratodus ?), and, with but a single 
exception (Ichthyophis),* among all other vertebrates. 
The larval lamprey is by this time a quarter of an inch 
long, yellowish white in colour; its movements are slug- 
gish, rarely more than to cause it to wriggle worm-like 
from the bottom. A few weeks later it has acquired its 
brownish grey colour, its fin fold is well marked, and its 
habit is active; it now feeds on muddy ooze rich in 
organic matter. It by this time possesses the essential 
characters of the well-grown larva, long looked upon 
as a distinct genus, Ammoceites. In its larval stage the 
lamprey appears to live a number of years; in Petromyzon 
planeri the adult stage is said to be sometimes deferred 
until the autumn of the fourth or fifth year. The trans- 
formation is then a surprisingly sudden one; the head 
attains its enlarged size, the mouth its ring-like and suc- 
torial character, losing its more anterior position, and its 
lip-like flaps (cf. Fig. 72, C,.D); teeth are developed in place 
of the numerous mouth papillz; gills, formerly simpler 
in character, opening directly from neck surface to gullet, 
now enter the branchial chamber, a ventral diverticulum 
of the gullet; eyes become prominent, complete their 
development, and attain the head surface; unpaired fin, 
formerly of great extent, is now reduced to its adult 
position and proportions. 
Il. Larval Sharks 
The larval history of Sharks has been summarized in 
Figs. 284-289: the younger of these stages (Figs. 284, 
285, 286) have not as yet escaped from their egg mem- 
branes. The hatching, in fact, of the young shark is 
* The writer has not confirmed Salensky’s observation upon the sturgeon. 
