4 BULLETIN OF THE BUREAU OF FISHERIES. 



The young of Bairdiella chrysura were taken in small numbers at intervals through- 

 out the latter half of June and the greater part of July. After the spawning season 

 began to wane very few young of this species were taken. The young of Anchovia 

 mitchilli were taken in considerable numbers throughout June, July, and August. 



BAIRDIELL.^ CHRYSURA. 



Spawning. — The eggs of Bairdiella chrysura were present in the plankton when work 

 was begun on June 9, and were taken in the tow net nearly every day after that date 

 until July 18, when they became relatively rare. Individual eggs were taken occasion- 

 ally as late as August 15. Eggs of this species were at no time abundant. They were 

 sufficiently numerous, however, to be readily obtained for study. They occurred in 

 greatest abundance during the last week in June and the first week in July. These two 

 weeks, doubtless, witnessed the height of the spawning season. 



Adult specimens of Bairdiella chrysura were frequently taken in small numbers in 

 the pound net and in the seine. Nearly all the adult fishes taken during June and July 

 had already spawned. On June 20 and again on June 27 a single female ripe for strip- 

 ping was brought into the laboratory. On the former occasion a few eggs were success- 

 fully fertilized. All of these eggs, however, died during early cleavage. 



Eggs. — The eggs of this species are spherical in form and 0.7 to 0.8 mm. in diameter. 

 The mature unfertilized egg is slightly yellowish in color. The yolk contains a rela- 

 tively large oil globule. After fertilization has taken place and the blastodisc has 

 become differentiated, the egg is almost perfectly transparent. The egg membrane is 

 thin and homy. Between the egg membrane and the delicate vitelline membrane 

 inclosing the yolk sphere there is a perceptible perivitelline space. The oil globule 

 normally rests near the upper pole while the blastodisc hangs at the lower pole of the 

 yolk sphere. The spherical form of the egg is maintained until the time of hatching. 



Segmentation. — In the mature unfertilized egg the yolk sphere is covered by a thin 

 layer of protoplasm. After fertihzation has taken place the protoplasm of this layer 

 becomes concentrated at the pole opposite the oil globule, where it forms a lenticular 

 cap on the surface of the yolk. This lenticular mass of protoplasm is the blastodisc. 

 The "streaming" movements which occur in the protoplasm as it becomes concen- 

 trated to form the blastodisc have been well described and figured by Ryder (1882) 

 for the cod " and more recently by other investigators for other species of teleosts. 



The fully developed blastodisc (fig. i, bd) is circular in outline. Its periphery fades 

 away almost imperceptibly into the very thin layer of protoplasm which remains at 

 the surface of the yolk sphere. No protoplasm is noticeable within the yolk except 

 in the vicinity of the oil globule. Here there is a small amount of protoplasm which 

 can hardly be detected in the newly fertiUzed egg, but which, as development advances, 

 becomes concentrated to form a protoplasmic cap covering about one-third of the 

 surface of the oil globule. 



Just before the first act of cleavage occurs one axis of the blastodisc becomes slightly 

 longer than the other. The first plane of cleavage cuts the blastodisc at right angles 

 to the longer axis (fig. 2). The second cleavage plane cuts the first at right angles 

 (fig. 3). The first two cleavage furrows are meridional and cut deeply into the 



o Ryder, John A,: Embryography of osseous fishes. Report United States Fish Commission 1883. p. 455-^05. 



