370 



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. 

 Even 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-brpwn. 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 lalielets. 

 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 only such points as seem relevant will be given. 



Crosses with Gasterosteus Mspinosus. 

 Besides the crosses already described between Gasterosteus bispinosus 

 and Fundulus heteruclitus, the following were attempted : 



Gasterosteus Mspinosus, 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. 



