Early Influence of Spermatozoan Characters of Echinoid Larvce. 131 



MATERIAL AND METHODS. 



One of the abundant reef sea-urchins at Montego Bay is the primitive 

 form Cidaris trihiiloides. The living egg of Cidaris is exceedingly transparent 

 and the union of the male and female nuclei may be followed in it without 

 difficulty; it may be fertilized readily in the laboratory with its own sperm 

 or with the sperm of other sea-urchins abundant in the vicinity, among these 

 being Toxopneustes (Lytechimis) variegatus and Hipponoe {Tripneustes) 

 esculenta. These crosses are easily made. The eggs may be fertilized at 

 once after their removal from the gonad, without artificial aid, although as 

 a check against the possibility of chance fertilization with Cidaris sperm 

 they were kept for 2 hours before making the fertilizations. A portion of 

 the eggs was always kept as an unfertilized control. 



Many investigators will recognize the convenience and advantage of 

 supplying developing larvae with an almost complete change of water from 

 time to time. I found it possible to do this by centrifuging the contents 

 of the finger bowls, which I used as aquaria, withdrawing the water from 

 above the larvae and replacing with fresh water. This method was used 

 only after the third day. This material was centrifuged only long enough 

 to throw the larvae down to the end of the tubes. The plutei treated in this 

 manner kept in better condition than those not centrifuged and thus not 

 given as complete a change of water. Owing to my limited time no attempt 

 was made to rear the larvae to metamorphosis. Every possible precaution 

 was taken to avoid chance fertilization or contamination of any nature of 

 the cultures. 



Since the completion of the investigation is being delayed by the pressure 

 of teaching it seems best to present at this time the results that were ob- 

 tained with the living material, leaving the cytological analysis of fixed 

 material for a later time. The outline figures used in illustrating the paper 

 are from camera-lucida sketches made from living larvae. 



INVESTIGATION. 



In its normal development Cidaris proved of interest, (i) because of its 

 slowness of development when compared with Hipponoe or Toxopneustes; 

 (2) in the difference in the site of its mesenchyme formation; (3) in the 

 place of the appearance of the larval skeleton. 



The anaphase of the first cleavage begins about 50 minutes after in- 

 semination. The cleavage is like that of other echinoids. The blastula 

 stage is reached in 16 to 18 hours, depending on the lot of eggs; gastrulation 

 begins in 20 to 23 hours; mesenchyme formation begins in 23 to 26 hours, 

 the mesenchyme cells arising from the inner end of the archenteron; chro- 

 matophores appear in about 44 hours; the enterocoele arises as a single 

 pouch in 44 to 50 hours; in 55 hours two enterocoeles may be seen, formed 

 by the division of the single vesicle; in 72 to 73 hours the beginning of the 

 formation of the skeleton may be noted. Even at this time, the beginning 

 of the fourth day, the body has not begun to assume the form of an echino- 



