192 ZOOLOGY. 



eggs being expelled mto the perivisceral cavity, and thence 

 finding their way out into the water through the interradial 

 slits.* The Ophiurans are bisexual, but one species being 

 known to be unisexual, viz., Ophiolepis squamata, accord- 

 ing to Metschnikoff. While most Ophiurans pass through 

 a metamorphosis, the young of Ophiolepis ciliata is developed 

 within the body of the parent, adhering by a sort of stalk 

 (Krohn). In Opliiopliolis bellis development is direct, there 

 being no metamorphosis. 



An Ophiuran which has accidentally lost its arms can re- 

 produce them by budding. Ltttken has discovered that in 

 species of Ophiothela and Ophiactis the body divides in two 

 spontaneously, having three arms on one side and three on 

 the other, while the disk looks as if it had been cut in two 

 by a knife and three new arms had then grown out from 

 the cut side. Simroth has made farther extended researches 

 on self -fission in Ophiactis. 



The Ophiurans in most cases undergo a decided meta- 

 morphosis like that of the star-fish, which will be described 

 at length farther on. The larva, called a pluteus, is free- 

 swimming, though in some species the young, in a modified 

 larval condition, reside in a pouch situated above the mouth 

 of the parent, finally escaping and swimming freely about 

 (A. Agassiz). 



In Ophiocoma vivipara Ljungman, which occurs in the 

 South Atlantic, the young at first live in the body of the 

 parent and afterward cluster on the surface of her disk. 

 The eggs are hatched successively, the young being found 

 in a regularly gradated series of stages of growth (Wyville- 

 Thompson). It appears probable, as in the case of the sea- 

 urchins, that the Ophiurans of the cooler portions of the 

 South Atlantic, in most cases at least, have no metamor- 

 phosis. Several native forms are also viviparous. 



Our most common sand-star is Ophiopholis bellis Lyman 

 {Fig. 135), which may be found at low-water mark, and espe- 

 cially among the roots of Laminaria thrown up on the 



* On the other hand, Ludwig denies that the eggs pass into the peri- 

 visceral cavity, but insists that they collect in pouches formed by an in- 

 troversion of the integument. 



