1893.] '^ [Hubbard. 



son of the axis of eggs as determined by the position of the yolk nucleus 

 shows that the axis of the egg has no uniform relation to the axis of the 

 ovary. 



Summary, 



1. This body originates from the nucleus in very small eggs in the 

 adult ; soon after the cell becomes fully ditferentiuted as an egg. 



3. It constantly moves from the nucleus towards the entodermic pole 

 of the egg which it reaches when the egg is ripe. 



3. It is situated at the entodermic pole of the egg at maturity and during 

 later stages. 



4. It is capable of growth condensing apparently when very young 

 and then continuing to grow to considerable size. 



5. It is of definite chemical composition, having great affinity for cer- 

 tain stains. 



6. It remains in the egg until the closing ot the blastopore and then 

 breaks up and disappears in the yolk. 



7. It is found in the eggs of many animals and has been figured as be- 

 longing lo the spermatogonium or male cell. See especially Zeit. fur 

 Wissen. Zool., Vol. li, Taf. xxxvi ; also Arkiv. fur Mikro. Anat., Vol. 

 xxxix, Taf. xxi. 



The majority of papers on embryology which mention this body dismiss 

 it without much comment. However, there are a few writers who at- 

 tempt to explain its function in oilier animals. The consensus of opinion 

 seems to be that it is the centre of yolk formation. But there is no direct 

 evidence that such is the case. It is mere speculation from the fact that it 

 is found in the protoplasm of the egg, belore the yolk is formed. In the 

 eggs of Cymatogaster I have never seen any evidence that it gives rise to 

 the yolk. The yolk globules are scattered through the protoplasm, seem- 

 ing to appear equally in all parts of the egg. As the yolk gradually 

 forms it is homogeneously distributed in different sectors of the egg until 

 maturation. Then the yolk collects at the entodermic pole of the egg, 

 ■where the yolk nucleus has become located long before. 



The close association which this body hus with the yolk would seem to 

 indicate that it is in some way connected with it. But how ? I think in 

 many of the eggs in which this body has been seen it is not at all func- 

 tional. But from the length of time it remains in the eggs of Cymato- 

 gaster and from the wonderful changes it undergoes in growth it would 

 seem to be functional in this egg. Dr. Eigenmaun has shown that these 

 eggs mature very rapidly and hence liavc a small amount of yolk. 

 This fact may account for the yolk nucleus remaining so long after seg- 

 mentation begins. If the egg matured very slowly and allowed tiie 

 formation of a large amount of yolk this body would probably disappear 

 before the egg is ripe, as it does in other fishes. 



Another interesting question arises as to what determines its position 



