OF THE PROTOZOA. CILIATA. 347 



In some species where fission proceeds on its simple type, food may con- 

 tinue to be received for a short period by the di\'iding animal. The small share 

 the abdominal contents within the cortical lamina have in the \'ital processes, 

 is shown by Lachmann's observation of a Stylonychia, " which, although a 

 considerable part of its chyme had been sucked out of it by an Acineta, still 

 imderwent division, so that one of the gemmules of division swam away from 

 it briskly, and only the other half of the old animal was destroyed." 



The direction of the line of section is perhaps, when longitudinal, usually 

 from before backwards, the constriction appearing fii'st and advancing more 

 rapidly at the head ; but the contrary, according to Stein, prevails in Chilodon 

 Cucidhdus, where the constriction makes its way solely from the posterior pole. 



When fission is transverse or oblique it necessarily involves the reproduc- 

 tion, in the posterior half, of the organs existing in the anterior, viz. the ciliary 

 apparatus of the head, the oral aperture, the tube prolonged from it, and the 

 contractile vesicle. So far, therefore, it approaches nearer the act of gemma- 

 tion than does longitudinal fission, wherein segments of the already existing 

 organs are separated for the piu-poses of the new individual, and are not 

 actually reproduced or created anew. " In those Infusoria," says Lachmann 

 (A. JSf. H. he. cit.), '' in which a peculiar series of stronger cilia leads to the 

 mouth (such as Oxytrkliince and Eiq)htece), the furrow in which this series 

 of cilia is situated is seen, subsequently to or simultaneously with the division 

 of the contractile vesicle, to become produced backwards over the mouth ; in 

 this prolongation cilia are produced, and its posterior extremity becomes 

 deepened into a mouth and oesophagus, which then opens towards the ali- 

 mentary cavity of the animal ; then, simultaneously with the external con- 

 striction of the body, the new fuiTow is separated from the old one. (In 

 Stentor the new fi^ontal series of cilia first makes its appearance on the old 

 animal as a lateral straight series — the crista lateralis of Ehrenberg). In 

 animals which also possess peculiar processes of the body as organs of motion 

 (hooks, styles, &c.), the fissation usually takes place in such a manner, that 

 each of the newly-formed animals acquires a portion of these from the old 

 animal, whilst the other part is of new formation." 



The manner in which self-division proceeds in Protozoa with a firm, and 

 seemingly almost brittle integument, is exemplified in Goleps (XXTV. 284, 

 285). Along the line of section a new secretion of chitinous substance takes 

 place, soft in consistence and transparent, which by its increasing width 

 separates the two portions of the original lorica ; in this interposed new 

 tissue a constriction presently manifests itself, and advancing in depth, the 

 two segments are finally simdered. It thus comes to pass that each product 

 of fission is one half covered with a dense shield, and the other half with a 

 soft, yielding integument. After a while, more molecules make their appear- 

 ance in the latter, which gradually assumes a firmness equal to that of the 

 old lorica. 



The Vorticellina, including the Ophrydina, do not divide until they have 

 assumed a sort of semiquiescent condition, by the complete withdi-awal of 

 their ciliary apparatus and the contraction of the body generally into a more 

 or less rounded or oval shape, — in short, until they have advanced one step 

 towards encysting themselves. 



Ehrcnberg portrayed their fission as a simple constriction advancing from 

 before backwards to separation of the body ; but Stein pointed out the actual 

 antecedents of the process. According to the latter writer, the head-portion 

 and its appendages withdraw ; the rotary organ is absorbed, and also the 

 oesophagus ; at the same time the contractile space vanishes ; the body ex- 

 pands in width, the nucleus outstretches itself across it, a constriction appears 



