BAIRDIELLA CHRYSURA AND ANCHOVIA MITCHILLI. 



15 



of Avchovia mitchilli are illustrated in figures 25, 26, and 27. Figure 28 illustrates an 

 egg in an advanced stage of cleavage in which the marginal cells of the blastoderm 

 are already cut off from the periblast. Eggs in this stage of development were usually 

 observed between 11 and 12 o'clock p. m. 



The germ ring (fig. 29, gr.) and the embryonic shield (fig. 30, es) are differentiated in 

 the manner described above in the eggs of Bairdiella chrysura. Soon after the germ 



Fig. 25. — Egg with blastoderm of 

 2 cells, lateral view. X 60. 



ANCHOVIA MITCHILLI. 



Fig. 26. — Egg with blastoderm of 4 cells, 

 surface view. X 60. 



ring is fully differentiated the blastoderm begins to grow around the yolk more rapidly 

 than in the earlier stages. The posterior pole of the blastoderm, however, does not 

 remain at a relatively fixed point, as is the case in many teleostean eggs, but recedes 

 as the anterior pole advances. As the blastoderm grows around the yolk, therefore, its 

 center remains at one pole of the major axis of the egg. The blastopore finally closes 

 at the opposite pole (fig. 34, hi). When the embryo is fully differentiated, therefore, 

 it lies approximately parallel with the major axis of the egg (fig. 35). 



pb-— 



ANCHOVIA MITCHILLI. 



Fig. 27. — Egg with blastoderm of 32 

 cells, lateral view. X 60. 



Fig. 28. — Egg with blastoderm in advanced 

 stage of cleavage: P^> periblast, X 60. 



In the majority of the eggs observed the blastopore closed between 4 and 5 o'clock 

 a. m. — i. e., approximately 10 hours after spawning. At this time the length of the 

 embryo is somewhat greater than half the greater circumference of the egg. Soon after 

 the closure of the blastopore, Kupffer's vesicle arises as a bubble-like body on the ventral 

 aspect of the embryo near its posterior extremity (fig. 35, Kv). The vesicle soon reaches 

 its maximum development and then gradually decreases in size until it disappears. 



