OF THE PROTOZOA. CILIATA. 351 



have their central portions occupied only by water. Hence we have in such 

 clusters a distinct proof of the extraordinary extent to which multiplication 

 by duplicative subdivision may proceed without the intei-position of any other 

 process. These animalcules, however, free themselves at times from theii- 

 gelatinous bed, and have been observed to undergo an ' encysting process ' 

 corresponding with that of the VorticelUna. It is much to be desii^ed that mi- 

 croscopic observers should devote themselves systematically to the continuous 

 study of even the commonest and best-known forms of these animalcules, 

 since there is not a single one whose entire life-history, from one generative 

 act to another, is kno^vn to us ; and since it cannot be even guessed at, with- 

 out such knowledge, what, among the many dissimilar forms that have been 

 described by Prof. Ehrenberg and others, are to be accounted as tnily di- 

 stinct species, and what are mere phases in the existence of others that are 

 perhaps very dissimilar to them in aspect, it is obvious that no credit is 

 really to be gained by the discovery of any number of apparently new species, 

 which shall be at all comparable with that to be acquii^ed by the complete 

 and satisfactoiy elucidation of the Kfe-history of any one." 



Gemmation (iUustrated by XXYII. 1-4 ; XXX. 17, 27, 29, 31, 33, 34).— 

 This is the next process of multiplication to be considered. It has much 

 analogy with fission, but is not nearly so widely diffused, being restricted 

 apparently to the families VorticeUina and OpTirydina, that is, to attached 

 species of Ciliata ; yet even among these it would seem not to be general ; 

 for Stein has failed to observe it in the genus Ojyercularia. In it a promi- 

 nence forms upon the surface, mostly near the posterior extremity, and of the 

 same granular homogeneous substance as the rest of the animal : a line of 

 constriction soon displays itself, and gradually deepens, whilst the budding 

 process increases in size and developes internal organs and external ap- 

 pendages, until, being sufficiently perfected for an isolated existence, it severs 

 itself from the parent stock. The gemma3 or buds thus produced are much 

 smaller than the parent, and, even when they have acquired theii' largest di- 

 mensions before separation, are less than the new beings originating from 

 self-division. In everj^ instance of fission the nucleus becomes di\ided be- 

 tween the two segments ; and some authors, as we have seen, hold the ojdI- 

 nion that these share between them a portion of other pre-existent organs of 

 the dividing animal ; on the other hand, in gemmation the bud is a mere 

 offshoot of the general substance, containing no portion of any pre-existing 

 organ — not even, so far as can be seen, of the nucleus ; and consequently all 

 the specially- organized parts are developed in it de novo. If the doctrine of 

 internal germs be admitted, then it may be imagined that each gemma origi- 

 nates from one of these, which takes on this external direction of development. 



On the completion of the gemma, we find that it resembles (except in Spi- 

 rocliona and Lagenophrys) a completely- contracted specimen of the parent 

 animalcule, and possesses, in lieu of the usual ciliated whorl on the head, 

 a posterior ciliary wreath, whereby, when detached, it swims freely away, 

 'wdth the posterior extremity, however, in advance. It resembles, therefore, 

 in all respects the product of fission when separated from its fellow, and, 

 like it, may either presently attach itself, losing its posterior circlet of 

 cilia, and acquire aU the characters of its parent — as well as, in process 

 of time, its dimensions, — or advance to a completely encysted state, prepara- 

 tory to a process of development, or simply for the object of preservation 

 from untoward external conditions. The act of gemmation goes on alike in 

 small and in large specimens. Stein notes its occuiTcnce in Vorticelke of only 

 ^"' in length. 



A few illustrations may render the above account of gemmation more clear. 



