392 Dr. C. F. Liitken on Spontaneous 



a special interest, because the Holothurida, Asterida, and 

 Ophiurida are the highest organisms in their sphere in which 

 a true spontaneous division has been ascertained or supposed 

 to occur; and as other forms of agamic reproduction, e.g. gem- 

 mation, are entirely unknown in the class Echinodermata*, 

 there is the less reason here than elsewhere to regard division 

 as a disguised gemmation or something of the kind. Sponta- 

 neous division, therefore, is manifested in this class of animals 

 with exceptional purity and independence. If we suppose that 

 it is really a division that takes place here, it is a division pure 

 and simple, and not a mask under which something else is 

 hidden (gemmation or some analogous mode of multiplication). 

 In fact, although spontaneous division has always been 

 represented as a special category of the various modes of 

 reproduction of the lower animals, especially as a subdivision 

 of agamic reproduction, and although the text-books assign 

 to this mode of reproduction a comparatively wide domain, it 

 is evident that in many cases the spontaneous division is only 

 apparent ; in reality it is often something quite different that 

 takes place ; and the part ascribed to this mode of reproduction 

 is thus so much reduced that it is easy to understand how doubts 

 may have arisen whether natural spontaneous division ever 

 takes place, with the exception, of course, of the animals placed 

 at the very bottom of the scale (Rhizopoda, Monera), in which 

 the notions of cell and individual are almost confounded, and 

 the individual, with the other properties of the cell, has also 

 inherited its divisibility. Thus, in many Infusoria, a "division 

 in the direction of the length " has been supposed in cases 

 in which there was only a copulation ; two individuals have 

 been found half united and half free, and it has been concluded 

 that they were in course of separation, while, on the contrary, 

 they were engaged in the no less astonishing operation of 

 fusing into onef. 



* In publishing a very interesting observation upon viviparity in an 

 Echinid (Anochanus), M. Grube (Monatsb. Akad. Wiss. Berl. 1868, p. 178) 

 has put forward the hypothesis that it was a case of agamic reproduction 

 by means of germs or internal buds ; but in reality there is no sufficient 

 reason for accepting this supposition, nor do I see how the difficulties 

 presented by the history of the reproduction of that Echinid can be 

 diminished by it. M. Grube's hypothesis, moreover, is connected with 

 the theory according to which the formation of the Asterid or Echinid in 

 the Pluteus-l&rva, is not a metamorphosis, but a gemmation — an opinion 

 the incorrectness of which I thought zoologists had long since recognized. 



t Besides this operation, which is the opposite of a division, there is 

 produced apparently in these animals a true longitudinal division of the 

 various bell-animalcules, which enables them to form colonies, when one 

 of the two newly formed bells does not detach itself. But it remains to 

 be learned whether this division, as in other Infusoria, is not in reality a 

 disguised production of two perfectly new individuals. 



