THE DEVELOPMENT OF AMPHIOXUS 5 



plate of the second polar division. The arched base of the clear 

 protoplasmic region lies about at the level of the equator, and 

 the whole space lies eccentrically toward that side of the egg 

 which, from later development, is known to be anterior or 



II 



FIG. 1. The egg of Amphioxus. C, after Cerfontaine, others after Sobotta. 

 A. Ovarian egg showing cortical plasm. B. Cortical layer forming a membrane 

 on the suface of the egg, within the vitelline membrane. C. Egg membrane 

 fully formed but still attached to surface of egg, D. Extruded, fertilized egg. 

 Membrane fully formed and beginning to leave the egg. c, Cortical layer; e, 

 endoplasm; m, egg membrane, externally vitelline, internally a product of the 

 exoplasm; p, perivitelline space; s, spermatozoon; v, vitelline membrane; /, 

 first polar body; //, second polar spindle. 



antero-dorsal. A diagram of a sagittal section of the egg is 

 shown in Fig. 2, in the position usually assumed by the egg in 

 the water. 



The spermatozoa are very small (15-20 micra in length); the 



