C&ap. I. WATER-SYSTEM. 17 



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 an individual 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 succeeded 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 specimens also shows very striking differences, and will always • enable 

 an observer to distinguish readily the larvae of the two species, even in their earliest 

 stages. Compare PI. III. Figs. 1, 2, 3, 4, 5, with Figs. 22-28 of Plate II. These 

 differences become more marked as they grow older, as will be seen when we de- 

 scribe adult larvae. In fact, the larva of A. berylinus 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. 1 



The principal points of difference in the young larva? 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 shortness; the small size of the oral extremity, when compared 

 to the anal, the latter being by far the most prominent. 



Water-system. — Before going on with the description of more advanced stages, I 

 will take up the development of the water-tubes at the point to which we had traced 

 them (PI. II. Fig. 28) in the larvae of A. berylinus. After the ends of the water- 

 tubes have extended beyond the oral opening (PL III. Fig. 4), the tubes increase 

 rapidly in diameter (PI. Ill Figs. 6, 8, w, vf), bending at the same time towards the 

 longitudinal axis (PI. III. Figs. 4, 5, 6, 8, 10, w, vf), the other extremity of the 

 tubes creeping round the stomach until they touch, but without uniting (PI. III. 

 Figs. 6, 8, 10, w, w'). The tubes at the oral extremity bend towards each 

 other (PI. III. Fig. 4), come in contact (PL III. Fig. 6), anS, soon after, a com- 

 munication is made, the water-system assuming the shape of an elliptical ring (PL 



1 Though we now consider the further progress of berylinus, and to A. pallidus for the older stages, 



development of our larvse in a different species from Had we presented these changes for a single species 



the first, we proceed without interruption, as the only, the one would have been defective in the be- 



phenomena of growth are identical in both ; and we ginning, the other in the end. As it is, our history 



link them here together only because our most com- is tolerably complete, the course and nature of the 



plete observations for the younger stages relate to A. changes being identical in both species. 

 vol. v. 3 



