33<j On Sj)ontaneoiis Division in the Echinodermata. 



That the faculty of regeneration is great in the Crinoids is 

 a well-known fact ; but as regards division we know no more 

 about these animals than about the Echinida, in which, indeed, 

 it could only occur in the Clypeastridte (Scutellinaj), which 

 are very flat ; for it is possible only Avhen the animal is con- 

 structed in such a manner that the deep wound produced by 

 this violent mutilation may cicatrize in a comparatively short 

 time, which also necessarily presupposes that the animal is 

 extremely tenacious of life, and endowed with a strong faculty 



single specimen of a species, e. g. Linckia ornithopiis, we cannot, of course, 

 draw any conclusion with respect to this. Now, in Astenas helianthus, it 

 seems to me to be beyond doubt that the number of arms is originally 

 small, and increases during the growtli of the animal ; and as this pecu- 

 liarity, so far as I know, has not hitherto been ascertained in any Echi- 

 noderm, I will here state in detail upon what I found my opinion. The 

 circumstance that the amis in the species in question are often of very 

 unequal length, leads one at once to conclude that some of them may be 

 yomiger than the others ; moreover it is frequently the case that some 

 arms (1, 2, or 3 &c.) are so short that the supposition that they have 

 been subsequently intercalated between the others acquires considerable 

 force; lastly, we sometimes meet with an arm of which the extreme 

 smallness and the awkward position (entirely on the ventral sm-face, in a 

 slightly dilated brachial angle) can leave no doubt that it is relatively 

 much younger than the rest. If we compare a certain number of speci- 

 mens of difi'ereut sizes (I have examined fifteen from 2 to 11 inches in 

 diameter) we acquire a general impression that the smaller they are the 

 fewer amis they possess. This rule, however, can only be taken in the 

 most general sense, and not as if the size and the number of arms consti- 

 tuted two completely parallel progressive series; but it is rarely that 

 several arms in a state of growth are united at the same point. The fol- 

 lowing Table shows that the smallest number of anns (23) occurs in the 

 smallest specimen, and the largest (41), which is nearly double the pi-e- 

 ceding, in a specimen which is only half adult : — 



From No. 1 to No. 7 the augmentation in the number of the arms goes 



