Chap. I. THE ADULT LARVA. 21 



symmetry of the Echinoderm larva, as contrasting directly with the radiate structure 

 of the adult animals. It appears to me that this interpretation of the form of the 

 larvae of Echinoderms is incorrect ;• they are radiate animals, and are no more 

 bilateral than a large number of Radiates exhibiting bilateral characters, such as 

 Arachnactis, the Ctenophorae, the Spatangoids, and the Holothurians, as will be shown 

 hereafter. 



The larvae figured on this plate (PI. III.) correspond to the larvae observed by 

 Van Beneden, and called by him Brachina ; the latter resemble more our larvas than 

 any figured by Miiller. I am strongly inclined to believe that Van Beneden's Bra- 

 china will eventually prove to be the larvae of the Asteracanthion rubens M. T., or of 

 a closely-allied species. The more advanced specimens of his Brachina began to show 

 signs of the brachiolar appendages, though Van Beneden did not notice them. See 

 Fig. 8 of the Plate accompanying his notice in the Bulletin de l'Academie des 

 Sciences de Belgique for 1850. These larvae are easily distinguished from ours by 

 the shortness and thickness of the arms, as well as the less elongated shape of the 

 larva. The time of breeding is also different; the European species spawning during 

 the end of March and beginning of April. The A. berylinus spawns in the last part 

 of July ; by the 26th no eggs could be found in any of the females, and the other 

 species (the A. pallidus) spawns during the third week in August. These facts are 

 additional proofs of the specific difference between our species of Asteracanthion and 

 the Asteracanthion rubens of Europe. 



"When seen in profile (PI. III. Figs. 9, 12, w, ww' ; PI. IV. Fig. 4, w, ww'), the 

 water-system runs in an arch, from the alimentary canal to the opening of the 

 mouth.; here the diameter increases, forming a reservoir {ww'), from which are 

 sent off small pouches (/' /'), leading into the brachiolar arms (//); the whole 

 of the oral opening is placed below the water-system. When seen from above 

 or below (PL III. Figs. 6, 8, 10, 11 ; PI. IV. Figs. 1, 2 ; PI. VII. Fig. 8) the 

 water-system is an elliptical ring tapering to a point in the odd brachiolar arm, 

 enclosing the stomach and oesophagus, which form, as it were, a solid axis to this 

 elliptical envelope. On one side of the stomach appears a large hole (PI. V. Fig. 

 7, h, anal part only; PI. VII. Fig. 8), the opening of a cul de sac of one branch 

 of the water-system passing between the stomach and the intestine. The portions 

 of the water-system extending along the stomach appear made up of distinct cham- 

 bers (PI. V. Figs. 6, 7, 8, w, w) ; these chambers are merely the result of an 

 optical delusion, arising from the greater or less flattening of certain parts of the 

 tube, this gives it the appearance of having been divided off into segments. 



The adult Larva. — The anal part of the larva, in its adult condition (PI. IV. Figs. 

 1, 2), has become pointed; the general shape is still somewhat rectangular; the 

 ventral and dorsal side are separated by a deep groove (PI. IV. Fig. 4), extending 



