382 



velopment. The heart usually diffei-entiates 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 A^essels, but I have 

 only in one in.'^tance observed either the heart or blood 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 doAvn. 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 of an eye. 



The ear may develop as a vesicle which in some cases shows otoliths. 

 Commonly this vesicle becomes must distended, appearing as a prominent 

 projection on either side. The car less frequently appears than the eye. 



The central nervous system may be laid dovpn, 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 tlie normal fish. 



If an embryo is laid rlowu at all it rarely occurs that pigment does not 

 develop, both on the yolk and in the body of the embryo. In some cases 

 this may be quite heavily developed, showing accumulations of large and 

 highly branched 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 



