ECHINOCYAMUS PÜSILLUS. 11 



»the first segmentation nucleus» a radiate arrangement, which extends 

 through the greater part of the yolk, PI. /, fig. 3. 



Not seldom I have seen several spermatozoa enter the Qg^., but 

 in such cases the eggs were always developed in an abnormal manner, 

 so that one gets aspects resembling those figured by Fol '). 



III. 



The segmentation of the ovum. 



All that is known with regard to the phenomena of segmentation 

 in the eggs of Clypeastroids is confined to the »Preliminary Observations» 

 on the development of Echinarachnius by Fewkes. However, seeing 

 that his description is brief and evidently not based on investigations 

 of the segmentation of the same ovum, and that, besides, the pheno- 

 mena of segmentation in Echinocyamus differ essentially in several 

 respects from those in Echinarachnius, it will not be out of place if I 

 communicate the results of my own investigations a little more in de- 

 tail. Of course, I have no intention of trying to give an account of the 

 internal phenomena of segmentation, viz. the metamorphosis of the nu- 

 cleus etc., but only of demonstrating the external characters of the 

 segmentation which I have been able to note on the living egg. 



Stadium loith two segments. 



The above mentioned radiate arrangement of the plasma sur- 

 rounding the segmentation nucleus becomes less distinct and is finally 

 not traceable. The round segmentation nucleus elongates somewhat 

 and assumes the well-known spindle form, PL I, fig. 4.^ the two poles, 

 as it often seemed to me, forming centres, each of a plasmatic radia- 

 tion not very distinct, PL /, fig. 5. About 25 to 35 minutes after the 

 impregnation the contour of the nucleus becomes almost invisible and 



1) Recherches sur la Fécondation et le commencement de l'hénogénie chez 

 divers animaux. — Mémoires de la Société de Physique et d'Histoire Baturelle de 

 Genève. Tome XXVI. 1. Genève 1877—1878. 



