14 BULLETIN OF THE BUREAU OF FISHERIES. 



taken before 8 o'clock p. m. Eggs were found occasionally in the early cleavage stages 

 as late as 9.30 o'clock p. m. Newly spawned eggs were taken in the tow net alike 

 on the flood and the ebb tides. 



Eggs. — The eggs of this species are not spherical, but slightly elongated. The major 

 axis, which is 0.65 to 0.75 mm. in length, is o.i to 0.3 mm. longer than the minor axis. 

 These eggs are almost perfectly transparent and contain no oil globule. Furthermore, 

 the yolk is composed of separate masses. It has the appearance under the microscope 

 of being broken up into large cells. As observed by Wenckebach " in 1886 and later 

 by other European naturalists, the elongated form of the egg and the segmented char- 

 acter of the yolk is characteristic also of the European anchovy (Engraidis encrasicholus). 

 The eggs of this species, however, are somewhat larger than the eggs of Anchovia mitchilli. 

 The difference in length of the major and the minor axes in the eggs of the former species 

 also is considerably greater. According to Heincke and Ehrenbaum '' (1900), the greater 

 diameter of the eggs of the European species is i.i to 1.5 mm., and the lesser 0.7 to 0.9 

 mm. These measurements approximate very closely the dimensions of the eggs of the 

 American species, Anchovia brownii. 



Eggs in advanced stages of development and newly hatched larvae were rarely- 

 taken in the tow net at the surface of the water. This fact suggests that before the 

 time of hatching the specific gravity of the eggs is increased sufficiently to cause them 

 to sink. This conclusion is verified by the results of experimental observations. Eggs 

 placed in a dish of sea water 12 to 16 hours after fertilization float at the surface for 

 several hours and then sink to the bottom of the dish. After hatching the larval fishes 

 may be found at any level in the dish. The eggs of this species are very delicate. When 

 placed in a dish of sea water many die before hatching. All the eggs alike, however, 

 sink to the bottom before any are hatched. 



Embryology. — The eggs oi Anchovia mitchilli, like those of Bairdiella chrysura, develop 

 in a manner typical for pelagic teleostean eggs, and the development differs from that 

 of Bairdiella only in a few unimportant details. The embryological development of 

 Anchovia mitchilli will therefore be discussed but briefly and with reference to the above 

 discussion of the embryology of Bairdiella chrysura. 



As indicated above, the eggs of Anchovia mitchilli are not spherical, but slightly 

 elongated. As the thin protoplasmic layer investing the yolk becomes concentrated 

 to form the blastodisc, the protoplasm "streams" toward one pole of the major axis. 

 When fully differentiated the blastodisc appears as a lenticular cap of protoplasm lying 

 on the somewhat flattened lower end of the yolk mass. The periphery of the blastodisc 

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

 at the surface of the yolk. Between the thin egg membrane and the delicate vitelline 

 membrane there is now a perceptible perivitelline space. 



Cleavage in these eggs advances with great regularity. It conforms in all essential 

 details to the process of cleavage, as above recorded, in the eggs of Bairdiella chrysura. 

 In many instances the early blastoderms in these eggs are even more symmetrical than 

 in the eggs of the latter species. Early blastoderms which are quite typical of the eggs 



1 Wenckebach. K. F.: De embryonale outwikkeling van de ansjovis {Engraulis encrasicholus). Verhandeling der Kaiser- 

 lichen Akademie van Wetenschappen. 1887. 



b Heincke. Fr.und Ehrenbaum. E.: Eier und Larven von Fischender Deutschen Bucht. II. Die Bcstimmuncder schwim- 

 menden Fishcicr und die Methodik der Einjessungen. Wissenschaftliche Meeresuntersuchungcn. n. f.. bd. in. Abteilung Helgo- 

 land, 1900, p. 127-332, taf. ix-x. 



