128 



MARINE ANIMALS OF MASSACHUSETTS BAY. 



Fig. 167. 



beginning of the back of the Star-fish (r, Fig. 166), from which the 

 spines will presently project. When this process is complete, the 

 whole embryo, with the exception of the part where the young 

 Star-fish is placed, grows opaque ; it fades, as it were, begins to 

 shrink and contract, and presently drops to the bottom, where 



it attaches itself by means of 

 short .arms (//', Fig. 166), 

 covered with warts, which act 

 as suckers, and are placed just 

 above the mouth. As soon as 

 the Star-fish has thus secured 

 itself, it begins to resorb the 

 whole external structure de- 

 scribed above ; the water-tubes, 

 * 4 the plastrons, and the compli- 

 cated system of arms connected 

 with them, disappear within the 

 little Star-fish ; it swallows up, 

 so to speak, the first stage of its 

 own existence ; it devours its 

 own larva, which now becomes 

 part and parcel of the new ani- 

 mal. Next the two surfaces, 

 the back and lower surface, on 

 which the arms are now marked 

 out, while the tentacles, suck- 

 ers, and spines have already 

 assumed a certain prominence, 

 approach each other. At this 

 time, however, the arms are 

 not in one plane ; both the back 

 and the lower surface are 

 curved in a kind of spiral ; they begin to flatten ; the arms spread 

 out on one level, and now the two surfaces draw together, 

 meeting at the circumference, and enclosing between them the 

 internal organs, which, as we have seen, are already formed and 

 surrounded by walls of their own, before the two walls of the bod) 



Fig. 167. Fig. 166 seen in profile, lettering as before. 



