EXPLANATION OF THE PLATES. 



(9) 



profile, to show the great development of the abac- 

 tinal area, and the Echinus-like arrangement of the 

 spines in tne young Starfish. The odd tentacle is 

 seen turned up, between two of the spines, with the 

 eye at its base. 



Figs. 3, 4, 5. Spines of the young Starfish in different 

 stages of growth. 



Fig. 6. An enlarged view of the terminal tentacle, to 

 show the position of the eye at the base of the odd 

 tentacle. 



Fig. 7. An enlarged view of the mesh-work of lime- 

 stone cells, to show the mode of formation of addi- 

 tional cells, by means of Y-shaped rods. 



Fig. 8. A greatly magnified figure of. a full-grown 

 Brachiolaria in its natural attitude, at rest, with the 

 Starfish almost ready to resorb the larva ; the obliquity 

 of the planes, in which the actinal and abactinal 

 pentagons are situated, is especially well seen in the 

 pointed anal extremity of this Brachiolaria. No let- 

 ters have been added to this figure, as the different 

 parts can readily be distinguished by comparing it 

 with PL IV. Figs. 1, 2, 4. 



PLATE VIII. 



Fig. 1. Young Asteraeanthion about one year old, seen 

 from the abactinal side. 



Figs. 2, 3, 4. Magnified views of spines (p), and of 

 rudimentary pedicellarise (p>, p"). 



Fig. 5. Odd terminal tentacle of a Starfish in the 

 stage of PL VIII. Fig. 10, at the extremity of the 

 arm, with the eye-speck («). 



Fig. 6. One of the abactinal water-tubes (d<) at the 

 angle of the rays. 



Fig. 7. One of the abactinal water-tubes (d 11 ) along the 

 edge of the rays. 



Fig. 8. Abactinal view of the arm of a young Star- 

 fish, probably two years old. 



Fig. 9. Actinal view of an arm of a young Starfish in 

 its third year. 



Fig. 10. Abactinal view of a young Starfish, in which 

 the rudimentary pedicellarise have made their appear- 

 ance, also having median and lateral lines of abac- 

 tinal water-tubes along the arm. Probably three 

 years old. 



Cambridge, Mass., December, 1864. 



