MUSEUM OF COMPARATIVE ZOOLOGY. 445 



body with stellate contour. Does this body correspond to the whole 

 amphiaster, or to only one of its halves 1 Does it result from a conden- 

 sation or from a division of the amphiaster 1 The second supposition 

 would appear a priori the more probable ; * but as I have never suc- 

 ceeded in seeing at the side of this stellate body another aster, I prefer 

 to adhere [?] to the first supposition." My criticism of the assumption 

 first suggested by Fol — a division of the first amphiaster — is perhaps 

 intelligible in the light of his first description. With this statement of 

 facts, it no longer serves as an explanation. I am, nevertheless, still 

 unable to accept the conclusions which Fol has reached on this point, 

 and believe that the phenomena are to be otherwise explained than by 

 assuming that either a division or a temporary consolidation of the first 

 amphiaster normally takes place. Without personal experience with 

 the animal under consideration it is fruitless to attempt any explana- 

 tion. Possibly Fol may have been less certain than he supposed of the 

 relative degrees of advancement presented by the stages compared, and 

 that, after all, the unique stellate body may have represented a condi- 

 tion antecedent to the first amphiaster, rather than subsequent to its 

 formation. The possibility of such an error is not, in view of the 

 necessary use of reagents, entirely improbable. The failure of other 

 observers to distinguish any corresponding stage in the metamorphosis 

 gives reason to think this may be due to an abnormal condition of the 

 eggs in which it was seen. 



In living eggs, when the polar globule begins to detach itself, the sur- 

 face of the yolk forms folds arranged like the rays of a star whose centre 

 is the peduncle uniting the globule to the vitellus. These folds become 

 more prominent as the globule detaches itself, and then fade away. This 

 and other phenomena — the elevation of a distinct pellicle in the forma- 

 tion of the polar globules — the author thinks are easily explained, if one 

 admits that the superficial layer of the yolk has a greater consistence 

 than the yolk itself Although this layer in certain respects deports 

 itself like a true membrane, in his opinion it is not such. 



There result from the internal half of the second archiamphiaster one 

 or two small clear spots, which present, when treated with reagents, the 

 aspect of young nuclei. They increase in size as they sink into the yolk, 

 and become fused together. Other clear spots appear at the "Side of the 

 first, and they too are fused with it to form the female pronucleus. 



Fol also reports the discovery of one (if there are two, the second has 

 escaped observation) polar globule in the sea-urchin. They are elimi- 



* It is the opinion previously adopted. See p. 436. 



