J. Wyman on some unusual modes of Gestation. 7 
gills had disa peared, but were replaced by internal ones which 
ged as usual on three hyoid arches. e development 
to its 
Wel nes here then a larva, in all of the details of its structure, 
especially in the existence of gills and of a flattened tail, adapted 
to aquatic locomotion and respiration, yet passing a portion of its 
time at least on the back of its parent pe at a distance from the 
ater. 
I was not able to ascertain whether the eggs were primarily 
deposited in the water or not, but it is well known to some of 
the colonists that after the larvee have reached a certain degree 
of development they are tig about in the manner just de- 
scribed and they do not w them under any other circum- 
stances. The existence of yolk cells in the intestine, shows that — 
for a period at least they may have from these a su ply nutri- 
ment. But after this is exhausted, and it appeared to be nearly 
so in those which I have dissected, how do they obtain their 
food? In the absence of limbs ad apted to terrestrial locomotion 
can they leave the body of the parent? and if they cannot, do 
they, asin the case of Pipa and probably in Notodelphys, depend 
upon a secretion from her? 
Among Fishes, as far as at present known, the external con- 
ditions under which the eggs are developed are more varied than 
in any other class of Vertebrates. There are scarce any known 
_ conditions of the higher classes to which there are not analogies 
~ at least in the class of fishes. Besides the ordinary mode of de- 
positing eggs upon the bottoms, some of the Salmonida, like the 
turtles, bury their eggs, the Lampreys (Petromyzon), the Breams, 
(Pomotis), the Hassars (Callicthys), the Stickle-backs (Gaster- 
ostei), &c., build more or less complete nests. Among some of 
the e Pipe fishes, agi nee the eggs and yp ew the 
and ‘other siardapiAl “pute, an “among some of the Sharks 
there is a vitelline placenta analogous to the Allantoidian one of 
the Mammalia.* 
* Prof. Owen (in Philos. Transactions, 1834,) has pointed out the vascular fies tions 
: of the foetal Kangaroo to the parent. The chorion ts not vascular, but the umbilical 
_ Vesicle is largely provided with blood vessels, and, as far as his investiga ons go, 
