MUSEUM OF COMPARATIVE ZOOLOGY. 241 
Four hours after an Agalma was placed in the aquarium, eggs in the 
4-cell stage were picked out of the water in which it was confined. I 
have traced one and the same egg from the 2-cell to the 4-cell stage, and 
find that it takes 2h. 10 m. for the necessary changes to be perfected in 
this growth. On another egg it was determined that it takes 45 m. to 
develop an egg in the 2-cell stage from an egg in which the germinative 
vesicle, or “nucleus,” had disappeared. By this observation it will be 
seen that it requires a little over an hour to pass from the egg just fertil- 
ized into the stage which exhibits the first sign of a primitive cleavage, 
plus the interval of time which elapses after the 2-cell stage is formed 
and before it begins to form the secondary furrow, or origin of the second 
cleavage-plane.* This last interval is probably not more than 30m. ; 
consequently the interval which elapses after fertilization before the 
formation of the primary furrow is about half an hour. 
Impregnation probably takes place in the gonophore. I have not 
been able to fecundate the Agalma egg artificially, nor was it seen to 
take place naturally. I have repeatedly tried to fertilize ova with sperm 
from the same colony, but have always failed. This fact led me, in 1880, 
to state that the animal cannot be impregnated by spermatozoa from its 
own male bells. Last summer (1884), however, to obtain some informa- 
tion on this point, an isolated Agalma was kept in a glass jar, and it 
dropped eggs which became segmented and later developed into primitive 
larvee. The water in which it was confined was not changed meanwhile, 
nor new liquid added. Of course this experiment does not absolutely 
demonstrate that the spermatozoa from the same colony can or cannot 
unite with an unfecundated ovum of the same, for sperm may have been 
in the water before the animal was placed there. Experimentation on 
the subject has many difficulties; but it must be confessed, that, as 
far as I have thus far gone in my studies, it looks as if the male bells 
of an Agalma may sometimes fertilize ova from the same axis. The 
great difficulty in the artificial fecundation of the Agalma egg was 
pointed out by Metschnikoff.* The ovum in the gonophore is enclosed 
in what he calls an “ Umhiillung,” from the walls of which the tender 
egg cannot be extracted without harm to its contents. 
The first naturalist to fertilize artificially the Siphonophore egg was 
Gegenbaur.f Metschnikoff t was equally unsuccessful with myself with 
* Studien iiber die Entwickelung der Medusen und Siphonophoren. Zett. /. 
Wiss. Zool., XXIV. p. 49. 
+ Beitrage zur niheren Kentniss der Schwimpolypen (Siphonophoren), p. 49. 
t Op. cit., p. 49. 
VOL. XI. — No. 11. 16 
