166 SYNOPTIC COLLECTION. 



tween the basals and terminals, and that the latter are 

 pushed' outward with the growing arms. These are addi- 

 tional plates and are not homologous with any plates of 

 the Crinoids. The anus in the young is near the edge of 

 the oral or actinal side. 



The arms at this time are broad, short, and unequal in 

 length. The ambulacra running out from the mouth have 

 two rows of organs which are like tentacles, being pointed 

 at the end. The madreporic body is near the edge of 

 the actinal side. As the starfish grows older, radial 

 symmetry predominates, and the five equal arms radiate 

 from the small central disc. The body becomes flat- 

 tened, and the spines and plates more or less irregular. 

 The monotony of the spiny upper surface is broken by 

 the little radiately-grooved madreporic body (No. 302) 

 which has moved from the actinal area and is at the junc- 

 tion of two arms on the abactinal side. The anus has also 

 moved and is near the center of the abactinal side. The 

 ambulacra carry four rows of organs which have devel- 

 oped suckers at the ends and become thereby efficient 

 locomotive organs. 



In the center of the ventral side is the mouth sur- 

 rounded by a membrane and guarded by five sets of 

 spines. 



Although the normal number of arms is five, it some- 

 times happens that only four are developed. On the 

 other hand in a collection of about eight hundred star- 

 fishes from Salem Harbor, there were, according to Mr. 

 N. L. Wilson, two six-rayed specimens and one seven- 

 rayed specimen. 



The power of the animal to reproduce lost arms is 

 shown in No. 303 where four arms have been lost, but 

 one has grown out to half the size of the fully grown 

 arms. No. 304 is probably a starfish that has been 

 wounded in some way. In trying to repair the injury it 

 produced the semblance of an arm. A specimen of this 

 kind is met with occasionally on our coast. 



