92 BULLETIN OF THE BUREAU OF FISHERIES. 



p. Egg about 1. 5 mm. in diameter, yellowish, opaque; oil globules 

 numerous, tmequal, grouped together; roots of threads scattered 

 over egg membrane. .Fundulus heierocliius (common killifish). 

 pp. Eggs smaller, i.i to 1.4 mm. in diameter. 



q. Egg I.I to 1.3 mm. in diameter, slightly yellowish, almost 

 transparent, held together by a tangle of coarse adhesive 

 threads; 12 to 20 unequal oil globules grouped together. 



Lucania parva (rainwater fish). 



qq. Egg 1.2 to 1.4 mm. in diameter, yellowish, highly transparent, 



held together by a tangle of very minute adhesive threads; a 



single large oil globule and groups of minute oil globules 



present Cyprinodon variegatus (short minnow). 



mm. Egg membrane adhesive, no threads. 



r. Egg about i mm. in diameter, yellowish, semitransparent, 

 glutinous, with a relatively large perivitelline space after 

 fertilization; oil globules small, unequal, scattered; embryo 

 with very little pigment up to time of hatching. 



Pomolobus csstivalis (glut herring). 



n. Eggs larger, 1.5 to 1.7 mm. in diameter, clinging together in a 



rather rigid mass. 



f. Egg 1. 5 to 1.7 mm. in diameter, yellowish, semiopaque; oil 



globules numerous, very unequal in size, mostly clustered 



at upper pole of egg. 



Gasterosteus aculeaius (three-spined stickleback). 



ss. Egg 1.5 to 1.6 mm. in diameter, darker and more opaque 



oil globules fewer in number and smaller than in the 



preceding. . . .Apeltes quadracus (four-spined stickleback). 



TAUTOGA ONITIS (Lionsm). TAUTOG. 



Spawning. — The principal spawning month for the tautog is June. Although 

 the majority of the fish taken after July i were spent, eggs were abundant in the 

 plankton as late as July 15. During the latter half of July they became gradually 

 less abundant, but were taken in small numbers as late as August 20. 



The tautog is prolific, but difficulty is experienced in obtaining eggs from captured 

 fish in quantities sufficient for successful fish-cultural operations. Little difficulty, 

 however, was experienced in obtaining and artificially fertilizing the eggs required for 

 embryological study. 



Eggs. — The eggs are highly transparent, spherical in form, and 0.9 to i mm. in 

 diameter. The egg membrane is thin and horny. The yolk sphere contains no oil 

 globule. The protoplasm which invests the yolk sphere in a very thin layer is finely 

 granular and hardly perceptible until fertilization has taken place and the process of 

 concentration that results in the formation of the blastodisc is initiated. As soon as 

 fertilization has taken place a relatively small space, the perivitelline space, becomes 

 apparent between the egg membrane and the delicate vitelline membrane which 

 incloses the yolk sphere. 



Blastodisc. — As soon as fertilization has taken place, the protoplasm becomes con- 

 centrated at one pole of the yolk sphere into a lenticular mass, the blastodisc. During 

 this process the protoplasm slowly flows toward the pole of concentration. The 

 "streaming" movements early described by Ryder " that occur in the protoplasmic 



oRyder. J. A.: A contribution to the embryography of osseous fishes * * * . Report United States Fish Commission 

 1882, p. 455-605. 



