PRELIMINARY GENERAL SKETCH 



189 



form during extrusion of the polar bodies. The two types just 

 described (Fig. 96) are connected by various gradations. Thus, 

 in the lamprey, the frog, the rabbit, and in Ainphioxus, one polar 

 body is expelled before, and one after, the entrance of the sper- 

 matozoon ; in the annelid OpJnyotrocJia, entrance takes place when 

 the first polar spindle is in the stage of the equatorial plate ; 



*"***. 



Pig. 95. _ Conjugation of the germ-nuclei and division of the sperm-aster in the sea-urchin 

 Toxopneustes, X looo. (For later stages see Fig. 52.) 



A. Union of the nuclei ; extension of the aster. B. Flattening of the sperm-nucleus against the 

 egg-nucleus ; division of the aster. 



