EMBRYOLOGY AND LARVAL DEVELOPMENT OF TELEOSTEAN FISHES. 419 



Soou after the closure of the blastopore, i. e., about 24 hours after fertilization, 

 melanin granules arise in some of these ameboid cells. These granules first appear in 

 the central region of the cell, i. e., in proximity with the nucleus, and gradually push 

 out toward the periphery or into the protoplasmic processes. Under high magnifica- 

 tion the movements of these granules may be readily observed. They are apparently 

 determined by the movements in the cytoplasm. 



In the course of a few hours after the appearance of the first melanin granules, 

 yellow pigment granules arise in some of the ameboid cells. Like the melanin granules, 

 the yellow pigment granules arise in ihe central region of the cell and later push out 

 toward the periphery. The movements of these granules are apparently identical 

 with those of the melanin granules. 



The phenomena involved in the development of chromatophores could not be as 

 satisfactorily observed on the embryo as in the extra-embryonic blastoderm. Pigment 

 arises in the chromatophores on the embryo simultaneously with the appearance of 

 pigment in the chromatophores in the extra-embryonic blastoderm. Furthermore the 



I.UC.KNIA P,\RVA. 



Fig. 28. — Egg 90 hours after fertilization. 



Fig. 29.— Egg just before hatching. 



chromatophores on the embryo, during the early stages of development, are cells of 

 essentially the same character as those in the extra-embryonic blastoderm. It is quite 

 probable that they arise in the same manner. Figure 25 is an attempt to illustrate 

 the distribution of chromatophores on the embryo and the extra-embryonic blastoderm 

 about 44 hours after fertilization. 



After circulation becomes well established the majority of the chromatophores in 

 the extra-embryonic blastoderm become aggregated along the larger blood vessels. 

 The distribution of chromatophores along the blood vessels in the extra-embryonic 

 blastoderm 68 hours after fertilization is illustrated in figures 26 and 27. 



As indicated above, the pigment granules arise in the central region of the cell and 

 gradually push out toward the periphery. Until pigment is present in all parts of the 

 cell the parts free from pigment remain clear. Even after pigment has been present 

 in all parts of the cell it may become concentrated in the central region leaving the 

 peripheral region clear. In many instances as the pigment becomes concentrated 

 isolated granules or groups of granules remain far out in the protoplasmic processes. 

 The concentration and redistribution of pigment granules is obviously not due to 

 ameboid movements of the cells but to movements of the pigment granules in the 



