332 Dr. C. F. Lutken on Spontaneous 



I have found two madreporic plates placed far from each 

 other in the large specimens of Asterias prohlema when the 

 regeneration was so far advanced that the younger group of arms 

 was scarcely behind the older one in devclo])ment. At the next 

 division, therefore, each half starfish would be furnished with 

 its madreporic plate. 



Whether the division always takes place at the same part 

 and in the same line, whether this changes in accordance Avith 

 definite laws as in the Medusa?, or, finally, whether there is no 

 rule in this matter, I am absolutely unable to say ; and I do 

 not think that this question can be cleared up until the spe- 

 cies under consideration has been thoroughly investigated in 

 the living state, for which, as it inhabits the north coast of the 

 United States of America, we shall, perhaps, not have long to 

 wait. It is much to be desired that such should be the case, 

 in order that we may know with certainty whether we have to 

 do here merely with a true division, or whether by it some 

 secondary pmiDOse is fulfilled. 



Asterias polyplax of New Holland, a species allied to A. 

 prohlema^ seems to present the same phenomena ; but I have 

 been able to examine only a few specimens of it. 



This mode of division is not known with certainty outside 

 the genus Asterias, nor even outside certain subdivisions of 

 that genus*. There are, as I have already indicated, a great 

 number of Asterids with multiple arms {Asterias aster, Ileli- 

 aster, Pycnojwdia, Sokister, AcantJiaster, Lahidiaster, Luidiaj 

 &c.) which do not present the least trace of this phenomenon. 

 On the other hand there are certain species of Ophidiaster and 

 Linckia which seem to be subject to another kind of division ; 

 but whether it is perfectly natural, or artificial (in the sense of 

 being provoked by some external violence), I cannot decide. 



in other specimens of the same or even larger size (15-18 millims.), and 

 even in a large specimen with six equal arms (43 millims. in radius). 

 Perhaps it may depend in part upon the season whether these organs are 

 or are not developed. In specimens of moderate or pretty large size I 

 have generally found the reproductive organs well developed in the older 

 arms, but wanting in the younger ones ; nevertheless in two cases (espe- 

 cially in the specimen represented in fig. l,o) they had attained more or less 

 development in the regenerated arms also. It would seem, therefore, that 

 this starfish is sexual (i. e. furnished with more or less developed sexual 

 organs) long before spontaneous division has terminated ; but it does 

 not follow that it is capable of reproduction before that time. 



• The Museum possesses a small specimen of CribeUa smiguinohnta 

 which so much resembles Astei-ias prohlema that for a moment I took it 

 for the latter ; it has three large and three small arms, exactly like A. 

 prohlema. It was brought up from a depth of 290 fathoms, to the west 

 of Hetland. 



