ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 863 



process of spawning under natui-al conclitions made at the tanks in 

 the Eothsay Aquarium. 



A perfectly ripe female set free in one of the tanks was in a few 

 minutes noticed moving slowly quite close to the bottom of the tank, 

 with four other fish making circles around her at some distance from 

 the bottom. Appearing satisfied with some stones which she had 

 been examining, she halted over them, and remained stationary a 

 few minutes about 1/2 in. from their surface, the tail being in a 

 straight line with the trunk and the pectoral fins near or resting on 

 the bottom. While in this position, a thin beaded ribbon was seen to 

 escape from the genital aperture and fall in graceful curves so as to 

 form a slightly conical mass. As the little heap of eggs increased, 

 the males continued circling round the spawning female at various 

 distances, while the other females in the tank remained apart. The 

 males kept from 8 to 10 in. above the bottom of the tank, and 

 formed circles ranging from 18 to 30 in. in diameter, with a peculiar 

 jerking motion of the tail as they performed their revolutions. Three 

 or four times during each revolution each fish expelled a small white 

 ribbon of milt, which fell slowly through the water, sometimes 

 reaching the bottom almost undiminished in size, but in most in- 

 stances they had almost completely dispersed before reaching the 

 bottom. In this way the whole of the water about the female 

 became of a faint milky colour, and practically every drop of it was 

 charged with sperms. Thus there is no attempt on the part of the 

 males to fertilize the eggs as they escape from the female, but only to 

 fertilize the water in the neighbourhood. By forming circles round 

 the female it does not matter how the currents are running.. 



Various experiments were tried to bring about an artificial 

 fertilization of herring ova, but the best results were obtained 

 when both male and female were held under water while the milt 

 and roe escaped, i. e. when the natural process of spawning was 

 followed. 



Development of Pelagic Fish-Eggs.* — A. Agassiz and C. 0. 

 Whitman report that they are now able to distinguish twenty-two 

 species of pelagic eggs, which it had before been difficult to know from 

 one another on account of their great resemblances. It has, however, 

 been found that the pigment spots on the surface of the yolk begin to 

 make their appearance at very difierent times in different species, and 

 there is a characteristic pigment-pattern. The eggs of six species of 

 flounders, two species of Coitus, of Clenolabrus, Tautoga, Osmerus, 

 and Lophius have been recognized. The number of eggs is very great, 

 bat the spawning seasons are comparatively short. 



As, in passing from IG-cclls to the 32-cell stage, the central portion 

 of the blastodisc becomes two cells deep, it is extremely difficult to 

 follow out the genesis of the individual cells in the living egg. 



With regard to their methods the authors state that the successive 

 phases of cleavage were first followed many times in the living egg ; 

 profile views and optical sections were obtained by tilting the Micro- 



* Proc. Amcr. Acad. Aits and Sci., xx. (1884) pp. 23-75 (1 pi.), 



