SOME PARTS OF THE SKELETON OF FISHES 277 
heterocercal tail of the embryo becoming homocercal in the adult, 
the tail of the latter was extremely heterocercal, far more so than 
that of many cartilaginous fishes. In fact, all that Vogt had really 
shown was, that the primitively homocercal tail of the embryo 
becomes gradually more and more heterocercal ; and he and others 
had been misled by the apparent homocercality of the adult fish into 
supposing that the heterocercality became lost again, whereas, in point 
of fact, it was only disguised. 
Consequently, Vogt’s observations did not prove in the least that 
a truly homocercal fish ever passed through a heterocercal state ; and 
as no observations respecting the development of the tail in what 
were supposed to be truly homocercal fish were extant, the doctrine 
that heterocercality precedes homocercality in embryonic life, was 
clearly not proven. On the other hand, until the development 
of some admitted homocercal fish had been examined, it was not 
disproved. 
Having procured a number of very young sticklebacks and eels, 
which would assuredly be admitted to be true homocercal Zeleoste7, 
if such things exist at all, I gladly availed myself of the opportunity 
of examining into this point. I was not a little surprised to discover, 
not only that these fishes are heterocercal in the embryonic state, 
but that they are perfectly heterocercal in the adult condition, their 
apparent homocercality being, as in the case of the salmon and its 
allies, a mere disguised heterocercality. 
In a Stickleback ths of an inch long (fig. 1), I found the 
gradually tapering extremity of the notochord (c) bent upwards 
at a considerable angle with the axis of the body, and terminating 
close to the superior rounded corner of the caudal fin. In the 
greater part of its extent it was enclosed neither in cartilage nor 
in bone—though bony rings, the rudiments of the centra of the 
vertebree, were developed in the wall of the notochord throughout 
the rest of the body. 
The last of these rings (0) lay just where the notochord began to 
bend up. It was slightly longer than the bony ring which preceded 
it (2), and instead of having its posterior margin parallel with the 
anterior, it sloped from above, downwards and backwards. Two 
short osseous plates (e), attached to the anterior part of the inferior 
surface of the penultimate ring, or rudimentary vertebral centrum, 
passed downwards and a little backwards, and abutted against a 
slender elongated mass of cartilage (g). Similar cartilaginous bodies 
occupy the same relation to corresponding plates of bone in the 
anterior vertebra in the region of the anal fin; and it is here seen, 
