EMBRYOLOGY OF TUE STARFISn. 



CHAPTER FIRST. 



ARTIFICIAL FECUNDATION, AND HISTORY OF THE DEVELOPMENT OF THE LARVA. 



Differences of the Sexes. — Since the existence of different sexual organs 

 in separate individuals was first pointed out among the lower animals, 

 the tendency of every additional advance in our knowledge of their struc- 

 ture has been to bring out more fully the differences of sex between them. 

 But recently, we did not even know that among the Medusce there were 

 male and female individuals; and yet, at the present day, it is a com- 

 paratively easy task to distinguish, among the larger Jelly-fishes, the 

 males from the females. The difference of coloring is very striking. The 

 spermaries of the males are often brihiantly tinged, while the ovaries of 

 the females are of duller hues. We thus find among Jelly-fishes the first 

 indication of an almost universal law in the animal kingdom, and which is 

 nowhere carried out to so great a degree as among Birds. A casual ob- 

 server could not fail to distinguish a male from a female Aurelia, — though 

 the great difference in the coloring of the males and females had not been 

 perceived by naturalists till it was first pointed out by Professor Agassiz, 

 in Aurelia flavidula Per. et Les. In Melicertum, in Turris, in Staurophora, 

 in Circe, a glance will sufiice to determine the sex of the individual ; 

 while a single look through a magnifying-glass will reveal to us the sex 

 of the smaller species, such as Eucope, Pennaria, Euphysa, and the like. 

 The difference of the sexes of some Echinoderms is easily perceived by 

 their difference of coloring at the time of spawning; among them are 

 our common Starfishes and our Sea-urchins. 



The males and females of our common species of Starfishes, Asteracan- 

 thion pallid us Agass. (A. vulgaris Stimp.F), and Asteracanthion berylinus 

 Agass., can readily be distinguished by their difference in coloring: all 



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