476 WESLEY R. COE, The maturation and fertilization of the egg of Cerebratulus. 



Pig. 50 ' ). M, caeca. The greatly elongated germ-nuclei lie in 

 contact with the cleavage-asters at their extremities. This is an ex- 

 ceptional case in which the cleavage - spindle is formed without the 

 complete fusion of the germ-nuclei. X 500- 



rig. 51 1) Cerebratulus leidyi. First polar spindle. Spermatozoon 

 with young aster. X ^00. 



1) It will be observed that Figs. 50, 51 are drawn at the same 

 magnification as Figs. 31 — 40. This will show the great difference in 

 size which exists between the eggs of these species of Nemerteans. 



