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yelopment. The heart usually differentiates and a pericardial cavity forms 
which commonly distends to enormous proportions. This has the effect of 
deforming the heart usually into a much elongated structure. The yolk and 
the embryo may in some instances differentiate blood vessels, but I have 
only in one instance observed either the heart or blocd vessels handling any 
blood. The result of this is that the embryo which may up to this period 
be quite normal in its developmental processes, has its food restricted to 
what may be directly absorbed from the yolk through other agents than the 
blood. That the embryo does thus obtain some food is evident from the 
progressive reduction of the yolk and the increased size, and the long con- 
tinued life of the embryo. 
The eyes in rare cases may be quite normal. From this condition all 
degrees of abnormalities obtain. The eyes are commonly too small, located 
too far forward and too low down. Often an eye is developed only on one 
side. The eye may be rudimentary to the extent of being only a large black 
pigmented area in the region of the forebrain. <A large proportion of the 
embryo develop no indication Gf an eye. 
The ear may develop as a vesicle which in some cases shows otoliths. 
Commonly this vesicle becomes niust distended, appearing as a prominent 
projection on either side. The ear less frequently appears than the eye. 
The central nervous system may be laid down, the brain even showing 
some of the primary divisions in the more successful embryos. 
The notocord is commonly present. The embryos may develop a varying 
number of somites, and quite commonly when these are present, some of 
the cells become contractile so that the whole embryo undergoes movements. 
The fins rarely appear, but in some instances the pectoral fins may be 
much larger than in the normal fish. 
If an embryo is Jaid down at all it rarely occurs that pigment does not 
develop, both on the yelk and in the body of the embryo. In some cases 
this may be quite heavily developed, showing accumulations of large and 
highly brauched chromatophores. In the better developed embryos a simple 
pattern may develop showing varying degrees of bilateral symmetry. 
The rate of development of the hybrid egg compared with that of the 
egg species. was noted in many instances. Comparative tables are given 
above in the detailed descriptions of the various hybrids. 
The earlier cleavage stages in every case was that of the species from 
which the egg was taken. This is true whether the rate of cleavage from the 
