MONOGRAPH OF THE EXISTING CBINOIDS. 611 



represented a single stage. A short time afterwards he revisited Toulon, and 

 this time he found that the comatulids all bore embryos at the same stage, which 

 were much less developed than the others. 



Observation of some comatulids in live cars at Villafranca showed that it 

 was rarely an opportunity offered to secure an isolated breeding animal, even at 

 the height of the breeding period. Two weeks would pass without any of the 

 animals breeding, but when one extruded its eggs the others generally followed. 

 There were therefore general breeding periods, followed by shorter or longer 

 periods of inactivity, during which none of the animals bred. 



At Naples Bury found that often several weeks would elapse without a single 

 fertilized ovum being obtained, and then suddenly several adults would be brought 

 in on the same day, each with a number of eggs on almost every pinnule. 



Seeliger found that in Antedon adriatica all the larvae of a given mother are 

 in the same developmental stage, this being particularly true in the earlier stages, 

 and that usually all of the larvae are liberated at the same time, about 124 hours 

 (four hours more than five days) after fertilization, no embryos remaining behind 

 undeveloped. But occasionally only a part of the larvae leave the pinnules, the 

 remainder following little by little until the seventh or even the eighth day, 

 although on the fifth day the stage of development of all the embryos had shown 

 but slight variation. 



For Antedon mediterranea Barrois and Bury give the length of embryonal 

 life as seven days. Sir Wyville Thomson records that of Antedon bifida as of 

 from three to four days' duration. 



The length of the free-swimming period is subject to much greater variation. 



Under unfavorable conditions a female after the breeding period may lose the 

 genital pinnules, parts of the arms, or even entire arms. Normally, however, 

 this self-mutilation never occurs, the female remaining quite intact. This loss 

 of pinnules and arms takes place especially in a deficiency of oxygen. 



Sir Wyville Thomson said that the larva possesses all the pecularities of 

 the sarcode organisms among the Protozoa and the lower forms of the ccelenterates. 

 Its external surface is richly ciliated and if lightly touched with a bristle it moves 

 off rapidly by means of these cilia in a direction opposite to the touch, giving 

 evidence of a high degree of irritability and power of automatic motion without 

 the slightest trace of a special nervous system. 



Seeliger found that larvae of the earlier fixed stages do not react to external 

 irritation, which agrees with his observation that no nervous system can be 

 demonstrated histologically. He notes that the nervous system of the young 

 stalked larva as demonstrated histologically does not suffice to explain its move- 

 ments under external irritation. Contraction of the calyx results not only from 

 touching the tentacles or disk, where nerve branches can be demonstrated, but 

 also from irritation of the aboral surface and of the stem where no nerve fibers 

 have as yet been found. 



Bather in 1894 mentioned "floating colonies" of Antedon bifida. In the 

 following year " Paddy from Cork " criticized Bather's " floating colonies " and 

 stated that this species lives clinging in numbers to stones below the low -tide mark. 



