362 



little to say since it fails to develop. I ha\e never seen any indication of 

 bloodvessels, either in the embryo or in the yolk so far as these could be 

 made out by circlulating blood. There is now and then an embryo that 

 shows what seems, from surface view, a little lakelet of blood. No corpus- 

 cles, however, can be seen, and I think they are only accumulations of a 

 pigment of some sort. Nevertheless a considerable portion of the yolk sub- 

 stance is absorbed. This is transferred to the embryo by probably the same 

 method as is employed prior to the development of the vascular system. 



The body of the embryo is always much too short and appears heavy. 

 The tail may develop to a considerable length, and in the more successful 

 individuals may show the caudal fin-folds with fine radiations. The body 

 lacks regularity of form and outline. Muscle segments develop, plainly 

 marked off by the brown pigment deposits along their borders. The muscle 

 segments are active, shown by the frequent movements of the tail. 



The eyes may be developed to varying degrees, or in many embryos 

 there is no indication of an eye. A quite common condition is the appear- 

 ance of only a single eye. Some of the embryos show an accumulation of 

 pigment cells either in two patches or one, which because of their location 

 and the fact that they are in rather well-circumscribed patches, probably 

 represent the eye. Two eyes are formed in many. These are always located 

 far forward, so that they seem set into the anterior surface of the head. 

 These may be quite large, well pigmented and showing a lens, or they may 

 be smaller, varying to a condition where merely two small pigment areas 

 are located on the very extreme anterior tip of the pointed head. 



The ear vesicle is usually formed. In the place where the vesicle should 

 be there is commonly formed, in the older embryos, an enlarged vesicular 

 structure. This, in some cases, is beyond doubt the enlarged ear vesicle. 



The embryos gradually die, but the better formed ones have lived for me 

 for ten days after the normals had hatched. 



Fnndulus JieterocUtus, female, 



X 



Tautogolahrus adspersus. male. 

 This cross was made five times. The percentage of impregnation may 

 be almost normal, as shown in experiment 36 in the following table : 



Experiment 28b 65 per cent . 



34b 17 " " 



36 90 " " 



102b 35 " " 



