296 
HENRY OBR. 
which my work has dealt there are probably no specific 
differences in the embryos. 
The developing eggs of this species of Amblvstoma seem to 
present a remarkable case of symbiosis. The eggs, surrounded 
by their gelatinous matrix, appear as a white mass floating on 
the surface of the water. (I found them in a small swampy 
pool on elevated ground.) In the first lot that I collected the 
medullary plates were just forming, and the two membranes 
surrounding each egg appeared perfectly homogeneous and 
transparent. In the second lot, collected some days later, the 
embryos were somewhat elongated, and the medullary canal 
had apparently just closed. In this lot the internal membrane 
of each egg was coloured a uniform light green by the presence 
in the membrane of a large number of minute globular green 
Algse. Neither in the spaces adjoining the internal membrane, 
nor in the external membrane, nor in the matrix, was there 
any colouration or trace of this Alga. The external membrane 
was transparent and the matrix white and translucent as before. 
In a third lot, collected when the balancers and gills had 
appeared, these conditions were the same, except that the 
Algje had increased in number and the colour was a much 
darker green. I have not discovered how the Algse enter the 
membrane, nor what physiological effect they have on the 
respiration of the embryo, but it seems probable that in this 
latter respect they may have an important influence. 
Clarke has given a detailed description of the external 
appearance and changes of the embryo of Amblystoma 
punctatum, so that for this part I may refer the reader to his 
work. As might have been expected, Amblystoma and Triton 
present much similarity in their development, while both differ 
in about the same degree from the Frog. The chief points of 
which I shall treat are the central nervous system, the hypo- 
physis, and some other parts and appendages of the head. 
The comparison of the embryos of the different groups affords 
some light in the attempt to explain the development of some 
of the more complicated parts. In order to avoid repetitions 
I have not separated the descriptions of parts which are inti- 
