124 



SEASON OF SPAWNING, AND EMBRYOLOGY. 



EGG OP THE STAR-FISH, AFTER 

 FERTILIZATION. 



cavity of the ray, the abactinal system \i. e., the sides and back of the 

 rays] being greatly expanded by the extraordinary development of these 

 organs." 



The two species common on the New England coast are Asterias 

 areniaola and Asterias vulgaris, and though much alike otherwise, they 



have different times of spawning — the former 

 (Massachusetts Bay to Florida) throwing out its 

 eggs a fortnight or more earlier in the summer 

 than the latter, whose range is more northerly 

 and hence in colder waters. Their period of 

 spawning, also, is very short, comprising only 

 three or four days. The eggs produced by the 

 females, as well as the spermatozoa sent out by 

 the males, find exit from the body through five 

 very small holes, in a series of large plates on 

 the back at the angles of the arms. Such eggs 

 as are fortunate enough to meet with spermato- 

 zoa in the water, before being overtaken by some form of destruction, 

 are fertilized, and immediately begin a very curious 

 series of changes in embryonic growth. 



This embryology, which has been described by Alex- 

 ander Agassiz, is like that of no other group of ani- 

 mals, but may be roughly compared to the transforma- 

 tions of a butterfly in the chrysalis. The larva which 

 hatches from the star-fish's egg is entirely unlike its 

 parent in form or structure, being an oddly -shaped, 

 ragged, transparent little creature, permeated through 



and through by water-tubes. When perfected, this larva 

 is called a hrachiolaria, and swims around for several 

 days by means of vibrating cilia, which keep it whirling 

 and bobbing about, not choosing its course, nevertheless, 

 by an exertion of its will, but a prey to all the chance 

 breezes and currents that can get it in their power. 



These larvae, says Mr. Agassiz, are to be found float- 

 ing in large numbers at night, though never by day, near 

 the surface, among cast-off skins of barnacles, which fur- 

 nish them with food during the time when they swim 

 freely about in company with multitudes of small Crus- 

 tacea, annelids, and hydroids. At such a time they are 

 fit food for shell-fish, and no doubt many fall into those 



AN EGG NEARLY 

 READY TO HATCH. 



AN EMBRYO STAR- 

 FISH AT AN EAR- 

 LY STAGE, SEEN 

 EDGEWISE. 



