EMBRYOLOGY AND LARVAL DEVELOPMENT OP TELEOSTEAN FISHES. 



421 



space is apparent between the egg membrane and the vitelline membrane. The micro- 

 pyle is relatively small. The yolk sphere contains a group of oil globules of unequal 

 size, varying from about 8 to 15 in number, which normally rests at the upper pole. 



Embryology. — The embryological development of these eggs conforms in all essential 

 respects to the course of development as above outlined for the eggs of Cyprinodon 



KIRTLANDIA VAGR.\NS. 



Fic. 32. — Egg with blastoderm of 2 cells. X so. Fig. 33. — Egg with blastoderm of 4 cells. 



variegatus. A detailed discussion of the embryology of this species would therefore be 

 superfluous. Successive stages in the process of cleavage and the differentiation of 

 the embryo are illustrated in figures 32 to 37. Early development advances somewhat 

 more rapidly than in the eggs of Cyprinodon. The embryo is well differentiated less 



KIRTLANDIA VAGRANS. 



Fig. 34. — Egg with blastoderm in advanced 

 cleavage stage. 



Fig. 35. — Egg with blastoderm showing germ ring 

 (GR) fully differentiated and an early stage in dif- 

 ferentiation of embryonic shield (ES). 



than 20 hours after fertilization. At 40 hours after fertilization (fig. 38) the embryo 

 is relatively large. It is segmented throughout and circulation is well established. A 

 few chromatophores are now apparent on the anterior region of the body. A few hours 

 later a relatively small number of melanophores arises also in the extra-embryonic 

 blastoderm. 



