508 H. H. Newman 



c The capsule surrounding the egg of F. heterocUtus is, 

 after exposure to water for some time, decidedly fibrous and 

 sticky, causing the eggs to clump up in a very disagreeable 

 fashion. The capsule of the F. majalis egg is, on the other 

 hand, scarcely fibrous or sticky and the eggs seldom clump. On 

 this account they are more easily handled than those of the other 

 species. 



d The size of the developing embryos and of young fish on 

 hatching is in the two species in proportion to the comparative 

 volume of the eggs, that of F. majalis being about twice that of 

 F. heteroclitus. 



e The color pattern of the young fish before and after hatching 

 is quite different in the two species, as are also the size and struc- 

 ture and pigment content of the chromatophores. 



4. Physiological Differences between the Eggs and the 

 Developing Embryos 



a The eggs and developing embryos of F. majalis, like the 

 adults, are much less resistant to unfavorable environmental 

 conditions than are those of F. heteroclitus. 



h The eggs of F. heteroclitus reach the hatching period in 

 about two weeks on the average, while those of F. majalis require 

 nearly three weeks on the average. As a corollary to this F. het- 

 eroclitus is at all stages of development markedly in advance of 

 F. majalis. The two species on hatching are at same stage of 

 development. 



c The body and yolk of F. heteroclitus embryos become 

 heavily pigmented after about three days of growth, while in 

 F. majalis only a very faint pigmentation occurs until after seven 

 or eight days. The color on the bodies of newly hatched young 

 is much paler in F. majalis than in F. heteroclitus. 



d The heart-beat of F. majalis is, stage for stage, much more 

 rapid than that of F. heteroclitus. 



e A fair percentage of hybrids from F. heteroclitus eggs hatch 

 spontaneously and are capable of living and thriving for months 

 while none of the hybrids from F. majalis eggs ever hatch. 



