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180 General Notes. [February, 
between the yolk y and the somatopleure, leaving the coelomic 
space c, which has been derived directly in the osseous fish 
embryo from the cleavage cavity of the egg, We thus find that 
the preexisting structure, from which the amniotic folds are 
formed in the higher types, is already present in the embryos of 
osseous fishes. The next important point to demonstrate is, at 
what grade in the phylum of the Chordata traces of amniotic folds 
first appear, and whether such rudiments of an amnion are also 
found in the embryos of osseous fishes. 
Glancing at 4, it will be seen that there are rudimentary amni- 
otic head and tail folds developed at a and a’, and that we, there- 
fore, have traces of an amnion appearing for the first time in 
embryos of the grade of osseous fishes. This is not universal, 
however, for it is found that in species in which the zona radiata 
z does not closely invest the ovum, the embryo Æ is not 
pressed down into the vitellus, so as to raise the somatopleure s 
into a fold or duplicature around the ends and along the sides of 
the embryo. The zona invests the ovum more or less closely in 
almost all Teleosts, but in a few, Alosa, for example, it does not, 
and in this species no traces of amniotic folds are ever developed, 
The embryo is differently conditioned in those eggs with the 
zona fitting closely around the ovum from those in which there 
either in the form of a rigid outer egg-shell, zona radiata z, or 
decidua reflexa dr, or even the walls of the uterine cavity 
itself, supposing, of course, that a large vesicular blastoderm con- 
taining yolk has been formed by epiboly. 
The gap between the truly epicyemate embryo, as seen in 
Alosa, and the endocyemate embryo of the Paratheria and 
Eutheria is, therefore, partly bridged by the presence of a rudi- 
mentary amnion, or amniotic folds in many teleostean embryos 
just prior to their escape from the eggs, or where the zona is 
ruptured. When this occurs the-amniotic folds vanish, as in the - 
embryos of many of the Salmonide, for example, anda closed amni- 
