184 



Many starfishes have large eggs, rich in yolk. It appears to be next to 

 impossible to obtain fertilization of such eggs, unless they are shed in the 

 natural way by the females. In this regard the Asteroids -- together with 

 the Holothurians are in remarkable contrast to the Echinoids, in which 

 large and yolky eggs are as easily fertilized as are the small, transparent 

 eggs, with little yolk substance. 



The development of the Asteroid-larva? generally takes a rather long 

 time, which fact partly accounts for the comparatively poor results 

 achieved in the rearing of these larvae. A stay of two three months in 

 some place is, in general, not long enough for obtaining satisfactory results 

 in the rearing of Asteroid-larvae. The fact that the main characters of the 

 larvae do not appear until they have reached their full size and are near 

 metamorphosis, makes this only more evident. The rearing of the young 

 larval stages alone does not serve to give much more than the proof that 

 the species in question has pelagic larvae, while in the Echinoids even the 

 first larval stage may give very important information of the larval 

 characters. 



To rear the young starfish from larva? in beginning metamorphosis, taken 

 pelagically, is generally easy enough, and much may certainly be achieved 

 in that way, under suitable laboratory conditions. But a fairly long time 

 will be necessary for rearing them far enough to identify them with cer- 

 tainty; this cannot be achieved during a stay of two three months. - 

 The experiments of Mead 1 ) showing how exceptionally rapid growth may 

 be in these animals, if a rich food supply is given them, while on the other 

 hand a poor food supply delays growth very considerably, is of special 

 interest in this connection. (That the food supply acts in the same way 

 on the larvae, accelerating their development when available in good 

 quality and sufficient quantity and delaying it when poor and insufficient, 

 is a well known fact, which I have also had a rich opportunity of observing). 



The lacking of a skeleton interferes in some way with the preservation 

 of Asteroid larvae. Not that they are difficult to preserve well, if carefully 

 treated; on the contrary! When taken up a little cautiously in a pipette 

 and then dropped directly into alcohol or formalin they will generally not 

 contract at all; even such forms as have long, contractile arms may be 

 preserved perfectly in this way 2 ). Thus far the Asteroid larvae are much 

 more easily preserved in a satisfactory way than Echinoid- and Ophiurid 

 larvae, which will nearly always contract as much as the skeleton allows. 



*) A. D. Mead. On the correlation between growth and food supply in starfish. American 

 Naturalist. XXXIV. 1900. (No. 397). 



2 ) Still better results may be achieved with such larvae if they are narcotized, by means 

 of magnesium sulfate, drops of alcohol or I he like, before they are killed. 



