COMPAEISON OF LAEY.E OF ASTEEACANTHION. 19 



Comparison of Larvae of Asteracanthion paUidus and A. hcri/limis. — Up to 

 this time all the larva3 described were raised by artificial fecundation 

 from eggs taken out of the ovaries of Asteracanthion berylinus Ag. 

 When I first discovered the larvse of our Starfishes, I immediately 

 examined the ovaries of our two most common species, the A. bery- 

 linus Ag. and A. pallid us Ag. I found that the eggs of the former 

 were not sufficiently advanced to be fecundated, while those of the second 

 species (A. pallidus) had all escaped. I am, therefore, positively certain 

 that all the larvte I am about to describe belong to the second species, 

 as they were all found swimming about previous to the time of spawn- 

 ing of the A. berylinus. As the interval between the time of spawning 

 of these two species is not less than three weeks, I had been able, during 

 this period, to make a general sketch of the whole development, from the 

 3'oungest larva found (PL III. Fig. 1), to the time when the Starfish is 

 formed, before beginning the artificial fecundation of the species just 

 described, the A. berylinus Ag. 



I thus obtained a general knowledge of the changes these larvae un- 

 dergo, and was enabled, when making the artificial fecundation, to pay 

 special attention to the develojjment of those parts, the origin of which 

 was not easily traced in older larvas. I was able in this way to carry 

 on, at the same time, the comparative study of the development of two 

 closely allied species, belonging, undoubtedly, to one and the same genus, 

 and to see how far differences could already be noticed in their early 

 stages of growth ; a glance at the figures of the young of one species (A. 

 pallidus Ag.) on Plate III., compared with the figures of Plate II. of the 

 second species (A. berylinus Ag.), will show how far the development- of 

 allied species diverges. What is particularly characteristic is the fact that 

 specific differences make their appearance so early. Soon after it became 

 evident that the embryos we were studying belonged to Echinoderms, it 

 was apparent that they were different species. The order of appearance 

 of the characters of the classes, the orders, the families, and genera, is one 

 of the greatest importance in a zoological point of view; and we owe to 

 Professor Agassiz to have pointed out, that the characters which make 

 their appearance first are by no means those which have been usually 

 supposed to take precedence ; in the present case we do not find it 

 possible to discern the class, the ordinal, the family, the generic and the 

 specific characters, in the order in Avhicli they are here mentioned. On 



