93 



S. Fish Commission where I had gone for the study of Ophiuran Era- 

 bryology, it was my good fortune to find that the eggs thrown by the 

 species of ophiuran found at North Falmouth, OpMura olivacea^ deve- 

 loped into larvae strikingly like those figured by Krohn. Owing to 

 the shortness of the breeding season only a limited supply of material 

 was obtained, but it is proving to be peculiarly favorable for the study 

 of several questions of Echinoderm morphology, which I hope to dis- 

 cuss in a future paper, the publication of which may, however, be 

 deferred for some time on account of the necessity of my filling in 

 some gaps in the earliest stages, hence the appearance of this preli- 

 minary note. 



The Species under discussion is found in abundance in the shel- 

 tered shallow water of the North Falmouth harbor where it lives in 

 the mat of dead and living grass and algae found on the bottom there. 

 It may be easily collectet by dredging with a long handled garden 

 rake from a row boat, the animals being brought up entangled in the 

 grass. 



Artificial fertilization was never successful and in order to get them 

 to spawn in the laboratory the ophiurans were placed in aquaria 

 dishes of fresh sea water. This method produced the desired result, 

 for, between 8 and 10 P. M. on July 16th, eggs and sperm were thrown 

 by animals brought in during the afternoon of that day. 



This early evening spawning is probably the rule with ophiurans 

 in general, as it was found to be the case in Jamaica species and the 

 one found at Nahant, Mass., OpMophilus aculeata. 



For echinoderms, the eggs of 0. olivacea are exceedingly large, 

 their size being due to the great amount of yolk they contain. They 

 are quite opaque and vary in color from green to orange yellow, the 

 eggs of one individual, however, are constant in their coloration. This 

 color presists until the larvae are quite well developed. 



Soon after fertilization the eggs throw off two membranes the first 

 being much thicker than the second. 



When thirty-six hours old the larvae are oval in shape, the axis 

 passing through the anterior and posterior poles being twice the length 

 of the transverse diameter. 



They swim actively by means of the coat of cilia which at this 

 stage covers their entire surface. 



The blastopore has been shifted from the posterior end of the 

 larva to a ventral position. This shifting is caused by the unequal 

 growth of the ventral and dorsal sides. 



From the blastopore protudes the end of a cellular mass of mate- 

 rial which almost fills the cavity of the archenteron and also extends 



