No. 3.] DEVELOPMENT OF lUAR/iVE 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 n", 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 

 egg 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. i). 



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 



