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tail is shown. Notocord and muscles are developed. A long tubular heart 
extends across the rather large pericardial sac. The body shows many 
finely divided pigment cells. These show, in general, a bilateral distribution. 
IXven this embryo is considerably too short. The contractions of the body 
are vigorous and frequent. The heart beats considerably slower than the 
normal. This embryo lived until the normals had hatched. 
The development of eyes, as in the preceding embryo, is uncommon. 
There are often pigmented areas which are probably the representatives of 
this organ, but no definite vesicles or cups. In many of the embryos the 
anterior end is occupied by enlarged vesicles which is more or less heavily 
pigmented. 
All the embryos are too short, many of them mere short masses of cells 
without any caudal elongation at all. They are all highly pigmented, the 
prevailing color being a reddish-brown. These cells are as a rule very finely 
divided. ‘The dark pigment cells are relatively few in number and are, 
as a whole, much less finely branched. I have never been able to see any 
bloodvessels that were carrying blood. In a few instances irregular lakelets, 
reddish in color, appeared, but I have been unable to detect any corpuscles 
in them. 
In addition to the above crosses it seems worth while to include the 
other crosses effected. To these much less attention was given so that in a 
description of them cnly such points as seem relevant will be given. 
Crosses with Gasterosteus bispinosus. 
Besides the crosses already described between Gasterosteus bispinosus 
and Fundulus heteroclitus, the following were attempted: 
Gasterostcus bispinosus, female, 
x 
Apeltes quadracus, male. 
In the single attempt to make this cross, only 17 per cent. of the eggs 
were impregnated. The eggs from a single female were used. It is probable 
that further attempts with more favorable females would yield a greater 
per cent. of impregnation. The fertilized eggs were normally impregnated. 
After the cleavage stages the hybrids fell behind the normals so that while 
the latter had closed the blastopore, the hybrids had encompassed the yolk 
about three-fourths of the way. Seven embryos were hatched and were in 
an apparently normal condition. These were kept alive for four days. 
