1893.] ^J- [Hubbard. 



ences to the literature on the subject is extensive, but, much of it l)eing 

 inaccessible to me, I have made no note of what I could not personally 

 examine. 



Van Bambeke ('83) studied this body in the eggs of Luciscus rutilus 

 and Rhodeus amarus. He says very little as to its origin, but thinks it 

 may come from the nucleus. His figures show it to be connected with 

 the nucleus by a funnel-shaped tube, the large end of which encloses the 

 nucleus and the small end touches the yolk nucleus. From this appear- 

 ance it would seem to be connected in some way with the nucleus. He 

 seems to think this body is the centre of the yolk elements. 



Balbiani ('83, p. 676) found this body in the eggs of Geophiles. In 

 these eggs the nucleus sends out prolongations. These break ofi" close to 

 the nucleus and in turn they break up into large granules. These lake a 

 deep stain. These granules, he thought afterwards, left the vitellus and 

 became the cells of the follicle. In this theory he was suppoiled by Fol, 

 Roule and Sabatier. There was one granule, however, that became 

 differentiated from the others, and instead of forming a cell of the follicle 

 remained in the vitellus and became what is known as the yolk nucleus. 

 He thought its function was to originate the yolk. He saj^s : "The first 

 granulations of yolk are produced on the surface of this body and after- 

 wards distribute themselves to all parts of the egg." In some animalshe 

 finds lines radiating in all directions from this body. Forming the limit 

 to these radiating lines are concentric layers of substance. 



Balfour ('85, pp. 21, 50) describes the yolk nucleus as seen in Araneina 

 by Ludwig and others. He says it always disappears before development 

 commences. He remarks tiiat it is probably connected in some way with 

 the nutrition of the ovum. This body is not found in all genera of 

 Araneina. 



Haeker ('92, p. 251) having studied this body in Aequorea forskalea 

 calls it tlie metanucleolus. In the ovarian eggs it was present within the 

 nucleus as the nucleolus. One half hour after being laid the nucleus ap- 

 peared to extrude this body. He traced the body in the blastomeres until 

 a late stage in cleavage. The author thinks homologous structures have 

 been seen in other Medusa?. He considers the paracopulation cells of 

 Daphnids described by Weismann and Ishikawa as homologous with the 

 melanucleus of Medusse. Haeker did not observe any division or any 

 radial arrangement of protoplasm anmnd this body. 



Monticelli ('92) has studied this structure in the ova o^ Dislomtim veli- 

 porum and D. richicardi. He concludes that the vitelline nucleus is a 

 cytoplasmic product, a nutritive diflereutiation probably acting as a centre 

 in the formation of yolk. 



PROC. AMEll. PHILOS. SOC. XXXIII. 144. K. PRINTED MARCH 3, 1894. 



