152 



H. l?EGINAI.n BULLER. 



IV. Remarks upon the Eggs and Spermatozoa of the 



ECHINOIDEA. 



The eggp, of the Echinoidea (as is also the case witli all 

 the Echinodermata) are surrounded by a thick, very trans- 

 parent, gelatinous coat, the zona pellncida, throuoh which 

 the spermatozoa have to make their way before they roacli 

 the living protoplasm of the egg. 



The following measurements from Echinus will give some 

 idea of the relative sizes of the living eggs, the gelatinous 



Tig. 1. — Etjjj of Ecliinus micro f.u here iilat, us. x 170. ». 

 Outline nl' protoplasm. A. Outline of zona peliuoida alter five 

 minutes in sea-water, c. Outline of zona pellucida after several 

 hours in sea-water, s. Spermatozoon. 



coat, and the spermatozoa : — Diameter of living vgg alone 

 O'll ram.; diameter of living egg and gelatinous coat 

 0'18 mm.; thickness of gelatinous coat 0*036 mm. ; lengtli 

 of a spermatozoon 0*051 mm. 



Each of the measurements just given is the average of ten 

 measurements. lUie eggs were measured almost directly 

 after being placed in water. 



The jelly increases in thickness after deposition of the 

 egg in sea-water. After twenty-four hours it is found to 

 have nearly doubled in thickness, and to have become 

 0*057 mm. wide. Tiie width of the jelly, which in the fresh 



