NO. 19.] ECHINODERMS OF CONNECTICUT. 77 



Owing to the nocturnal habits of the animals the eggs of at 

 least some of the species are discharged in the evening; that is, 

 between sunset and midnight. They are set free in the water 

 and are there fertilized by spermatozoa from another individual. 

 After fertilization the egg develops into a free-swimming ciliated 

 larva, which by a complicated metamorphosis gives rise to the 

 young ophiuran as described in the following chapter. 



The genital bursae are thin-walled sacs ; and, as the sea water 

 contained in them has free access to the exterior through the 

 genital slits, and can be continually changed by the contraction 

 of the disk, the bursae serve as respiratory organs in addition to 

 their primary function of discharging the genital products. The 

 minute tentacles of the arms also aid in respiration. 



DEVELOPMENT 



In most species of ophiurans the genital products are simply 

 discharged into the sea water, and abandoned to their fate. In 

 the little Amphipholis squamata, however, the eggs are retained 

 within the body of the parent until the embryonic development 

 is completed and the little ophiuran has reached the form of 

 the adult. Moreover, in this case, a nourishing exudation is said 

 to be poured out upon the eggs, which supplements the store of 

 food contained in the yolk. 



This species is likewise hermaphrodite, both ovary and sperm- 

 ary being attached to each of the genital bursae. After the young 

 have reached the adult form, the whole disk of the parent, with 

 the exception of the mouth frame, may sometimes be thrown 

 off to allow the young to escape, and then be regenerated. The 

 breeding habits and development of this species have been studied 

 by Fewkes* and others. 



In the majority of ophiurans, the sexes are separate, the eggs 

 being thrown out into the water, and fertilization takes place 

 whenever suitable sperm cells are in the vicinity. 



The eggs segment by a regular cleavage, as in the starfish 

 and sea-urchin. As in these two groups, the embryos quickly 

 develop into free-swimming larvae, which in this class are called 

 plutei, and which often feed for several weeks at the surface of 



• Bull. Museum Comparative Zoology, vol. xiii, 1887. 



