440 CASWELL GRAVE 



that those echinoderms in which various pecuHar methods of 

 brooding are found, are just those which produce a compara- 

 tively small number of very large yolky eggs, viz: Cribrella, 

 Amphiura, Cucumaria, etc. 



When brooding has been established in a species a correla- 

 tion between yolk content of egg and period of larval develop- 

 ment such as that which exists in those forms which have pela- 

 gic eggs and larvae may disappear because there is then no 

 further necessity for haste, on the part of the brooded eggs, 

 to assume the adult condition. Protection against the dangers 

 of the developmental period in such cases is assumed by the 

 parent. For this reason, in practically all cases of brooded 

 eggs, the species fails to conform to the correlation curve. 



BREEDING HABITS OF OPHIURA 



None of the numerous attempts which have been made to 

 fertilize the eggs of Ophiura artificially have been successful, 

 but it has been an easy matter by following the method out- 

 lined below, to induce Ophiura to spawn in aquaria in the labora- 

 tory during its breeding season which, at Beaufort, North Caro- 

 lina, extends over the months of June and July.^ 



Method. At the tune of low tide about thirty adult animals 

 are collected from among the roots of eel grass and sedimentaiw 

 debris on the shallow flats of Beaufort Harbor and are placed 

 in an aquarium jar of about ten liters capacity. In order to 

 keep the animals under conditions as nearly normal as possible 

 until near the time of day when spawning has been found to 

 take place (shortly after twilight), the jar containing them is 

 placed in running water (suspended beneath a wharf) until 

 about sunset. The animals are then transferred to the labora- 

 tory, placed in another aquarium jar of fresh sea-water and 

 allowed to stand undisturbed before a window. 



For a time after this transfer the animals may be observed 

 to huddle together near that side of the aquarium least illumi- 



3 The earliest date on which a set of mature eggs has been secured is June 

 5, the latest, Julv 2G 



