20 EMBRYOLOGY OF THE STARFISH. 



the contrary, the specific characters are early stamped upon the embryo, 

 and did we but know how to recognize individual differences among the 

 lower animals as well as we can already in some of the Fishes, we might 

 find that with Echinoderms, as has been shown for Fishes by Professor 

 Agassiz, the stamp of individuality is very early impressed upon the 

 embryo. Long before we can tell that a young Perch belongs to the 

 genus Ctenolabrus, we can already say with certainty whether it will be 

 colored red or gray or brown or green. 



The time of spawning of Starfishes is very short, as, three or four days 

 after the A. berylinus began to spawn, it was quite difficult to find females 

 with eggs ; and a week after the beginning of the spawning, I never suc- 

 ceeded in finding a single one. Owing to this great difference in the 

 time of spawning and its short duration, there can be no doubt, from the 

 date at which I first caught the Starfish larvae floating about, to which of 

 our two species they belong. A careful comparison of the youngest speci- 

 mens also shows very striking differences, and Avill always enable an 

 observer to distinguish readily the larva3 of the two species, even in their 

 earliest stages. Compare PI. III. Fiffs. 1, 2, 3, 4, 5, with Figs. 22-28 of 

 Plate 11. These differences become more marked as they grow older, as 

 will be seen when we describe adult larvte. In fact, the larva of A. bery- 

 linus is pear-shaped, with the thick end at the oral extremity, while in 

 the larva of A. pallidus the thick end of the equally pear-shaped, but 

 relatively shorter body is at the anal extremity.* 



The principal points of difference in the young larvae of this second 

 species (the A. pallidus), from those previously described, are differences 

 of -proportions. The larvae of the A. berylinus are elongated cylindrical ; 

 the oral extremity is somewhat broader and more prominent than the 

 anal. The larva of A. pallidus can at once be recognized by its short- 

 ness ; the small size of the oral extremity, when compared to the anal, 

 the latter being by far the most prominent, 



• Watcr-System. — Before going on with the description of more advanced 



* Thougli we now consider the further progress of development of our lars'se in a different species 

 from the first, we proceed without interruption, as the phenomena of growth are identical in both ; 

 and we link them liere together only because our most complete observations for the younger stages 

 relate to A. berylinus, and to A. pallidus for the older stages. Had we presented these changes for 

 a single species only, the one would have been defective in the beginning, the other in the end. As 

 it is, our history is tolerably complete, the course and nature of the changes being identical in both 

 species. 



