332 WILSON AND MATHEWS. [Vol. X. 



III. The Maturation and Fertilization of Asterias 

 FORBESii. The Fertilization of Arbacia punctulata. 



A. The Maturation of Asterias forbesii. 



The following description of some of the phenomena of the 

 ovarian maturation of the starfish Q%g is based upon the study 

 of a single ovary, which, fortunately, exhibited clearly the 

 various stages of ripening until the complete formation of the 

 first polar spindle. Owing to the difficulty of obtaining ovaries 

 in maturation it has been impossible to establish these obser- 

 vations by the study of other similar specimens ; but from eggs 

 matured artificially, either by the action of sea-water or by 

 vigorous agitation, it has been possible to confirm most of the 

 essential facts and to extend the study through the whole 

 process of maturation. 



The eggs and ovaries throughout have been fixed in corrosive 

 sublimate-acetic solution, a fluid which seems to yield particu- 

 larly fine fixation of this material ; and sections have been 

 stained upon the slide by iron-haematoxylin, followed either by 

 Congo red, Bordeaux red, or, in a few cases, by acid fuchsin. 

 By this method, and in such material, the origin of the centro- 

 somes, the history of the chromatin, and the origin and fate 

 of the nucleolus may be followed with great clearness. Of the 

 chromatin and nucleolus many novel things have been learned, 

 which are reserved for a more detailed description. The origin 

 and fate of the centrosomes are, in a paper of this nature, of 

 particular interest, and their history is accordingly given at 

 some length. 



The artificial maturation of the echinoderm &gg by rapid 

 agitation, first pointed out by Morgan, ^ is a matter of such 

 interest that I present the following observations in confirma- 

 tion of his result. It will be found on placing unripe eggs, 

 after a vigorous shaking, in sea-water, that a large proportion 

 of them now extrude the polar globules, and the first globule 

 often again divides. Such eggs, when unfertilized, do not, 

 however, and could not be induced to, develop further, clearly 



1 Anat. Anz., IX. 



