No. I.] 



THE ECHINODERM EGG. 



323 



Fig. I. Diagrams from successive camera drawings of the living eggs of Tox- 

 opneustes. In all, about seventy such cases have been continuously observed. 

 The original position of the egg-nucleus is shown by the circle containing 

 a reticulum marked ?. E, the entrance-point of the spermatozoon and the 

 entrance-cone ; M, meeting-point of the pronuclei (egg-nucleus dotted); C, cleav- 

 age-nucleus (with parallel lines) in its ultimate position ; the subsequent axis of 

 the cleavage-amphiaster is shown by the line passing through the nucleus, the 

 poles of the spindle by small circles at its ends. 



The paths of the pronuclei are indicated by the curved arrows, successive posi- 

 tions of the egg-nucleus by dotted circular outlines, those of the sperm-nucleus 

 by black dots. The definitive egg-axis is shown by the straight arrow, the point 

 of which is turned toward the pole opposite to the micromere-pole. The dotted 

 line {,F) indicates the plane of first cleavage (in B it is vertical, coinciding with 

 the arrow indicating the egg-axis). 



A and B are diametrically opposed in polarity, though agreeing closely in other 

 respects. C and D are also diametrically opposed in polarity, but differ consider- 

 ably otherwise. 



