334 Dr. C. F. Liitken on tSjwntaneous 



necessarily tliat when such a Linckia or Ophidiaster (with 5 

 or 6 arms) divides, or, what is the same thing, throws off or 

 loses its arms, it will give origin, under favourable circum- 

 stances, to as many new Asterids as it possessed arms, per- 

 haps even to one more if the disk is equally endowed with the 

 faculty of regeneration. I have found in the same species 

 such " comets " of small size and also of considerable dimen- 

 sions. When the disk and the new arms were still but little 

 developed, there was no madreporic plate ; in the contrary case 

 I have always found two, one on each side of the principal 

 arm. If we assume that this division is entirely spontaneous, 

 it would be the first known example of a true natural division 

 being more than binary and producing directly and at once a 

 multiplicity of new individuals — the first tnie example of the 

 ^' divisio radialis " of Hackel. That this polymerous divisi- 

 bility cannot serve to support the singular theory proposed by 

 Duvernoy and taken up by Hackel and other authors, accord- 

 ing to which the Asterida and Ophiurida are compound 

 animals, is quite evident. 



It may be further remarked that we may also meet with 

 specimens of other Asterids which at the first glance remind 

 us of the comet-shaped Linckice and Ophidiastres : I have 

 myself found examples of Astenaf; ruhens of this kind with 

 1 large arm and 4 small ones in course of sprouting ; and Sir 

 John Dalyell* represents several of them which he kept alive 

 for some time ; but, so far as I can judge from my own expe- 

 rience, this case is not precisely the same as the preceding, as, 

 in fact, in A. ruhens the disk remains, and it is by this and 

 not by the single arm, as in Linckia omithopus and Ophi- 

 diaster cribrarius^ that the new arms are regenerated. From 

 this it follows that if an Asterias ruhens lost all its five arms, 

 none of them could continue to live or regenerate the complete 

 animal ; how far the disk alone might be capable of doing so, 

 I do not know. I must add, however, that I have met with 

 some very young specimens oi Asterias prohlema in the " comet- 

 form," in which the five or six small arms had the appear- 

 ance of having been regenerated from the extremity of the 

 only arm which had been detached, and consequently I cannot 

 deny that a polymerous division may also take place in that 

 species f. 



* It does not appear with equal clearness from all the figures that the 

 disk continues attached to the oldest arm ; and, to judge from the manner 

 in which he expresses himself, the author does not seem to regard this 

 as necessary. Similar regenerated specimens are represented by Forbes 

 and Fredol. 



i" M. Hackel also has found two specimens of Asterias tenuispina with 

 this comet-like form ; and at the meeting of naturalists at Christiania in 



