OF ARTS AND SCIENCES : APRIL 14, 1863. 113 



figure (Fig. 13), in which the embryo is seen in profile. This figure repre- 

 sents it fi-om the mouth side. We see on the left of the stomach the open 

 curve of the tentacles (st), while on the other side the beginning of the 

 abactinal region (r) is visible. The tentacles are formed, as is clearly- 

 seen in this figure, by the folds of the walls of the water-tube of one side ; 

 while the abactinal area (r) is developed on the surface of the water-tube 

 placed on the opposite side. The large opening (w) on the right of the 

 stomach is a branch of the water system which passes out on the opposite 

 side, under the intestine, between it and the stomach. 



Fig. 13 is Fig. 12, seen in profile. It shows the course of the vibratile chord, 

 the position of the rudimentaiy tentacles (*7) of the young star-fish, the 

 shape of the oesophagus (o) and its position, hanging down between the 

 Y shanks of the water system. The position of the branches of the water 

 system (/') which pass into the brachiolar tentacles is also clearly seen. 



Fig. 14 is a young star-fish (^A. pallidus), a few hours after it has absorbed the 

 Brachiolaria. Its irregular outline is apparent. The arms are not yet all 

 in one plane ; the young star-fish is not yet unwound. 



Fig. 15. The S9,me as Fig. 14, seen fi-om the actiual side to show the rudimen- 

 tary character of the tentacles (t), which are simple loops opening into 

 a wide cavity. The mouth (??«) of the young star-fish is movable. In this 

 and the preceding figure the spines are simple warts, with accumulation of 

 Y-shaped limestone particles. They are, however, arranged in regular 

 order ; the outer rows of each arm have four spines, the next three, then 

 two, and finally a central one. 



Fig. 16. A young star-fish much more advanced than Figs. 14 and 15, in 

 which the arms are on one level, the spines quite well developed, and the 

 tentacles extending far beyond the edge of the disc, provided with suckers. 

 We see in this particularly well the crinoidal arrangement of the plates of 

 limestone particles on the abactinal side. The arrangement of the spines is 

 still regular. There are no signs of the madreporic body or of the anus on 

 this abactinal side. 



Fig. 1 7. The lower side of a young star-fish in about the condition (not quite 

 as advanced) of Fig. 16, to show that the terminal tentacle (t', Fig. 16) 

 never develops a sucker ; but at the base of this odd tentacle, which always 

 remains cylindrical, even in the adult, we find an eye-speck (e) placed on 

 a prominent bulb. The other tentacles, as is seen in the same figure, have 

 all suckers, and are arranged in one row on each side of the radiating tube. 

 The position of the madreporic body (b) is still on the lower side, opening 

 in the angle between two of the arms, as is seen in this figure. 



Fig. 18 is a young star-fish seen in profile, to show the arched abactinal area 

 and the mode of carrying the odd ocular tentacle (f), which is always 

 turned up. The spines are very prominent for the size of the star-fish, 

 and in this attitude the young star-fish would readily be mistaken for a 

 young sea-urchin. 



12* 



