342 WILSON AND MATHEWS. 



sperm, or in the first cleavage-asters, at any time, though the 

 asters are large, perfectly distinct, and in the anaphase of the 

 first cleavage the structure of the archoplasms may be seen 

 with striking clearness. This failure to demonstrate centro- 

 somes cannot be due to faulty method, for the centrosomes of 

 the polar spindles have been recognized in their infancy, traced 

 in their growth, and clearly followed to their respective ends. 

 In Arbacia there are at no time any radiations in the mature 

 Q^g other than those proceeding from the sperm-archoplasm. 

 In Asterias where the egg-centrosome and its archoplasm are 

 to be seen, the latter may be followed in its steps of disinte- 

 gration until it passes from view long before the union of the 

 two nuclei. Finally Fol's picro-osmic mixture when employed 

 upon Arbacia eggs, as in Toxopneiistes, conclusively shows that 

 the colorless aureole figured by Fol is an artefact caused in 

 large part by the destruction of the archoplasm which should 

 occupy this space. This aureole was readily obtained, yet 

 within it, among the shreds and tatters of the archoplasmic- 

 mass, no pictures of centrosomes resembling those of Fol 

 could be obtained. 



Biological Laboratory of Columbia College, 

 New York, December ii, 1894. 



