4i8 



BULIvETIN OF THE BUREAU OP FISHERIES. 



day of incubation the embryo becomes segmented throughout and circulation is estab- 

 lished. An attempt is made in figures 26 and 27 to illustrate the course of the larger 

 blood vessels in the extra-embryonic blastoderm 68 hours after fertilization. 



A late stage in the development of the embryo is illustrated in figure 29. It is now 

 relatively large, its length exceeding the circumference of the egg. The yolk mass is 

 materially reduced and the embryo is free to move within the egg membrane. 



.•V.i.i/..""' 



LUCANIA PARV.V. 



FlO. 



-Egg 24 hours after fertilization; KV, 

 Kupffer's vesicle. 



Tig. 25. — Egg 4S hours after fertilization. 



Pigmentation. — The eggs of Lticania parva afford very favorable material for the 

 study of the development of chromatophores. While the embryonic shield is becoming 

 differentiated, cells which maj' be recognized in the living material by their refractile 

 properties proliferate from its inner margin and from the inner margin of the germ ring 

 and become sparsely scattered over the blastoderm. These cells are irregular in outline 

 and usually send out a relatively small number of slender protoplasmic processes. They 



LUCANIA PARVA. 



Fig. 26. — Egg 68 hours after fertilization, 

 viewed from the dorsal aspect of the 

 head of the embryo. 



Fig. 27. Egg 68 hours after fertilization, 

 viewed from the anterior aspect of the 

 head of the embryo. 



undergo slow ameboid movements which involve form changes of the cell body rather 

 than marked extension and retraction of protoplasmic processes. These cells at first 

 appear isolated. Before the embryonic axis is well differentiated many of them are 

 apparently connected by their protoplasmic processes and form a syncytial network 

 which involves the entire e.xtra-erabryonic area of the blastoderm. Some of the ameboid 

 cells still remain isolated. 



