No. 3:] DEVELOPMENT OF MARINE SPONGES. 343 
the two nucleoli present in the developing egg are lost, one 
after the other, at the time when the egg reaches its full size. 
As to how the first of the two is lost, I have no evidence, but 
the second nucleolus may often be seen lying just outside the 
nucleus in the yolk, Fig. 105 7”, showing that it has been ex- 
truded from the nucleus. The nucleus differs in size so little 
from the yolk balls, and the latter stain so deeply, that I was 
at first in doubt whether to claim the object seen just outside 
the nucleus as an extruded nucleolus, or to regard it as merely 
a yolk ball. But so many eggs showed this one very deeply 
staining sphere in about the same position, that I was finally 
convinced it could be nothing less than the extruded nucleolus. 
Very rarely an egg much less than the full size is found with 
but a single peripherally placed nucleolus, indicating that the 
first nucleolus has already been lost. But this is a rare excep- 
tion, the rule being that the nucleoli disappear only after the 
ege attains its full size. The nucleus which remains after the 
extension of the nucleoli, Fig. 105, has a membrane and finely 
granular contents which stain feebly. 
My observations on the formation and loss of the nucleoli 
were made in the Bahamas in the fall of 1888. On my return 
I found that Fiedler (5) had just described the same phenom- 
ena in Spongilla, and regarded the two small nucleoli as polar 
bodies. Fiedler finds that the two small nucleoli are constricted 
off as buds from a larger central one, the latter remaining after 
the extrusion of the former. Further, at the time when the 
nucleoli are extruded, the nuclear membrane disappears. There 
are thus some differences of detail between our accounts. In 
the interpretation of these bodies as polar globules I cannot 
agree with Fiedler, because they are formed (though not dis- 
charged) long before the egg reaches its full size. Moreover, 
polar bodies of the ordinary metazoon type exist within the 
group of sponges, as is shown by Magdeburg’s discovery of 
them in Plakina trilopha (see the notice of Magdeburg’s unpub- 
lished observations in Korschelt & Heider, p. 1). 
The segmentation of the egg of Tedanione is total, and regu- 
lar, at any rate as regards the first two planes. In Pl. XXIII, 
Fig. 106, is shown the stage of two segments, and in Fig. 107 
