The British % Guiana Museum. 223 
begin to shrivel ; the hind limbs grow out and then the 
front limbs ; and the tail is gradually absorbed and 
eventually vanishes in the adult frog, by which time the 
gills have quite disappeared, the slits closed up, and the 
lungs are in full breathing order ; and the heart now not 
only drives blood to be purified, but also drives the puri- 
fied blood to all parts of the body. The development, how- 
ever, is not always so complete. In some forms of the 
group, limbs are never developed ; in others, the tail is 
retained during life ; in others, again, external gills are 
always present with lungs. The frogs and toads, in which 
the development is complete, are the highest forms of the 
group and depart most from the fish-like stages in adult 
life. Their history, however, shows their relationship to 
the class of fishes. In Pseudis, the tadpole or frog-fish 
grows to an extremely large size, being about nine inches 
in length (the specimens exhibited are much smaller), 
and is so perfe6lly fish-like, as to be easily mistaken for 
a fish. When this is allowed to develop, a frog eventually 
appears of about one-fourth the size of the full-grown 
tadpole — hence the term paradoxus. 
In the front part of the case, by these Amphibia , are 
shewn a few embryo mammals, such as a foetal horse, 
calf, and dolphin, together with a small puppy born with- 
out fore legs, and a four-legged chicken and duckling. 
Beneath are shewn various forms of colonial fishes in 
spirit, such as the eleftric eel, the sucking-fish, the half- 
beak etc., already mentioned, together with dried speci- 
mens of several kinds, many already referred to. Among 
them are to be seen a very small specimen of the 
curious hammer-headed shark, with its curious trans- 
versely elongated head, like a hammer on the end 
FF2 
