MEMOIRS OF THK NATIONAL ACADEMY OF SOIENCES. 85 



Tlie usual color of the species is an olive green, with darker bands ou the arms and somotiines 

 with a clouded disk. 



Tlnough tlic hleiidinjj of their colors with the seaweed the oi>hiuraiis arc fiicatly ])n)tected 

 from their eneuiies, and it is dilhciilt, even wlieu looking for them, to see tliem among tlie seaweed 

 so long as they do not move. 



It is quite common to find a small Am|)hiiiod crustacean clinging to tlie arms of dredged 

 specimens, and from the structure of the crustacean it is probable tliat the two siiecies live 

 together conimensally. What benefit either animal can derive from the association it is diflicult 

 to see. 



One pair of the thoracic legs of the crustacean is so modified as to form a structure beauti- 

 fully adai>ted for clinging to the round ophiurau arms. The last segment but one of each of this 

 pair of legs is Y-shaped. At the end of one arm of the Y is attached a movable segment, tlie end 

 segment of the leg, which when shut down upon the end of the other arm of the Y incloses a 

 triangular space in which the ophiurau arm is held. 



The body of the crustacean is colored and banded in such a manner as to simulate closely the 

 color and banding of the ophiurau arms. 



When placed in aquaria with their host, the crustaceans cling to the ophiurau arms until the 

 water becomes depleted of oxygen, when they leave the arms and swim about the edge of the dish 

 apparently much alarmed. 



In examining the stomachs of the oiihiurans one finds bits of other animals, such as crustacean 

 appendages and the skeletons of young horseshoe crabs. P>om this it is probable that the crea- 

 tures are scavengers, since an active crustacean would hardly be captured l>y so slow and poorly 

 armed an animal as an ophiurau. None were ever observed to eat anything when kejit in the 

 laboratory, and it is quite out of the question to observe them in their natural habitat, siuce they 

 are nocturnal animals remaining hidden during the day. 



The ophiurans were first examined for sexual elements early in June, and at that time the 

 eggs were very large but- adhered closely together in the gonads. The sperm appeared to be fully 

 formed bnt were uonmotile. 



From this time ou until the middle of August the species was regularly watched and exam- 

 ined, and on July 16 the first ripe eggs and sperm were obtained. A great number of specimens 

 had that day been dredged and placed in a(iuaria dishes of fresh, filtered sea water. One week 

 later a great number of adults were again brought in and ])laced under the same conditiims as 

 those which had spawned in the laboratory the week before, but this time very few eggs were 

 obtained, and all subsequent attempts to get the ophiurans to spawn wer(^ unsuccessful. 



From this it would seem that the breeding season is extremely short.' 



The time of day at which spawning occurred corresi)ouds well with the time at which I have 

 noted it to take place in Oiihiophilus avulvuta and Ophiocoma erhiiiulii, that is, between S and l(t 

 o'clock p. m. 



PHYSIOLOGICAI, NOTES. 



The locomotor movements of an oiihiurid, upon a casual observation, seem to consist of an 

 uncoordinated writhing and twisting not calculated to bring the creature to food or a place of 

 safety e.Kcept by chance; but a more carefiil study shows them to be the result of an orderly and 

 nicely coordinated mechanism. 



The rapid strides which characterize the movements of a brittle star are in strong contrast 



' During tlio summer of 1S99, after tliis paper liad f;ono to press, my expciionce with the speiies was viiy dif- 

 ferent from tlie alpuve. 8peciiii<>ns brought intu the laboratory early in Juu(^ threw eggs and sperm, Imt the eggs, 

 after passing thnmgh the i-arly segmentation stages, ceased to develop. The eggs wno probably iiiimatnri', and 

 were spawned only beeauso of the bad condition of the water in the aqnaria, bnt spawning always oecurred early 

 in the evening at the timc> when it would have occurred uudiT normal conditions. Why unri|ie eggs should dev<lop 

 at all, or why eggs mature enough to begin their develojjment should not be mature enough to complete it, is au 

 interesting (lucstion. 



This phenomenon was repeated every few days until .Inly L'(!, wIumi about oni'-l'ourth the number of eggs 

 spawned developed into normal larva'. This is ten days liilir than the date when eggs became mature at Woods 

 IIoll. Krom the fact that the wati'r is much warmer at lieaufort than at Wooils I loll one would expect to lind the 

 spawning season earlier at the latter place. 



loaoe — 2 



