OPHIUEA BREVISPINA 441 



nated but as dusk comes on they become active, crawl about 

 over the bottom and attempt to cHmb the side of the jar. At 

 about eight o'clock spawning begins. The spawning process 

 is initiated by the males, but very soon after sperm has been 

 emitted into the water the females begin to liberate eggs. 



The presence of sperm, or of some substance associated with 

 the sperm, in the water of the aquaraium containing the females 

 seems to be the necessary stimulus to egg laying. In the 

 presence of a greatly diluted solution of the spermatic secretion, 

 such as may be assumed to be present under normal conditions 

 in the open sea, it is probable that mature eggs only are extruded 

 by the females, but in aquaria the water becomes clouded 

 with sperm, and, as if overstimulated by this unusually large 

 amount of sperm, the females throw out their entire content 

 of eggs, the immature with the mature. 



It is difficult fully to test this conclusion since there is no exter- 

 nal character by which the males of Ophiura may be distin- 

 guished from females. The conclusion rests upon the obser- 

 vation that in those cases when it has happened that the number 

 of males placed in an aquarium has been few, a much larger 

 per cent of the eggs then secured has been mature than in cases 

 in which the number of males has been large.. 



A female, while extruding her eggs, either stands upright, 

 supported by the side of the aquarium, or with her body held 

 horizontal to and high above the bottom by her strongly arched 

 arms. While the body is thus elevated the eggs pass from the 

 distal openings of the genital bursae into the water and slowly 

 rise to the surface, their appearance at this time being like that 

 of ascending streams of minute bubbles of air. 



This peculiar position of the body of the female during the 

 spawning process, (and it is sometimes assumed by the male 

 also) has been observed in species of Ophiurid other than Ophiura. 

 It may be accounted for as an adaptation by which these ani- 

 mals, which live just beneath the surface of the bottom or under 

 conditions such that their bodies are covered for a considerable 

 part of the time by surface debris, provide for the unobstructed 

 passage of their eggs into the free water above, where condi- 



