MATURATION, FERTILIZATION, AND POLARITY 

 IN THE ECHINODERM EGG. NEW LIGHT ON 

 THE "QUADRILLE OF THE CENTERS." 



EDMUND B. WILSON and ALBERT P. MATHEWS. 



No cytological paper of late years has aroused more general 

 interest than that which contains Fol's remarkable account of 

 the " Quadrille of the Centers " in the echinoderm egg. Brief 

 and insufficiently illustrated as that paper is,^ it contains not 

 only very explicit statements of observed fact, but also what 

 seems to be strong internal evidence of their accuracy. We 

 were accordingly led to reexamine the phenomena, not with any 

 expectation of reaching results contrary to those of Fol, but 

 in the hope of confirming and extending them. The investi- 

 gation was begun by the senior author in the case of Toxo- 

 pneustes variegatiis, Kg., a form in which the eggs are of glass- 

 like transparency in life, and yield brilliantly clear pictures 

 in sections. Many of the phenomena can in this species be 

 followed in the living egg, and important data were thus ob- 

 tained regarding the paths of the pronuclei and their relations 

 to the future cleavage-planes and to the polar differentiation of 

 the egg. (See Part I.) In serial sections (especially after 

 fixation by sublimate-acetic and staining on the slide by iron- 

 haematoxylin, followed or preceded by Congo red, Bordeaux red, 

 or acid fuchsin) every step in the fertilization can be followed, 

 without a gap, from the moment of entrance of the spermato- 

 zoon up to the cleavage stages, and with a clearness such that 

 all the essential features can easily be studied in micro-photo- 

 graphs (looo diameters), of which an extensive series has been 

 prepared. In the meantime, Mr. Mathews made a parallel and 

 independent examination of the fertilization in another species 

 of sea-urchin {Arbacia ptmctulata, Gray), and also in a star-fish 

 {Asterias Forbesii, Verrill), the eggs of the latter form being 



1 Anat. Atiz., VI, 1891, and Arch. Sci. Phys. et Nat.. XXV, 1891. 



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