348 GENERAL HISTORY OF THE INFUSORIA. 



on its anterior border, and, extending constantly in depth, at length effects its 

 complete division. When the section has reached the third of the body, a 

 conical space displays itself towards the anterior portion of each half (XXYII. 

 3), lined by a special membrane, covered by cilia on its posterior side or base, 

 which are seen to vibrate within the cavity. This formation is the rudiment 

 of the futiu^e rotary organ. The apex of the conical hollow is prolonged by 

 a canal which eventually opens on the sui-face, and thus establishes a con- 

 tinuity between the lining membrane and the external integument. At the 

 same time the internal angle at the base of the cone is j)roduced inwards so 

 as to form the ahmentaiy tube. When these changes are accompHshed, the 

 body is half cut through, and the appearance is rather that of two indi\-idual 

 animalcules united posteriorly, having their ciliary apparatus retracted, and 

 the peristom contracted in a splinter-like manner over it. Lastly, the 

 advancing act of scission divides the nucleus ; and the whole body becomes 

 resolved into two individuals seated upon the same stalk. From this account 

 it follows, that, of the original organs of the animalcule, the nucleus is the 

 only one divided between the two resultant beings by the process of fission ; 

 all the rest are formed anew out of the homogeneous substance of the body, 

 viz. the peristom, the rotary organ, the alimentary tube, and the contractile 

 vesicle. 



This absorption and renewal of parts during fissation is denied by Lachmann, 

 who affirms that the movement of the cilia upon the ciliary apparatus, and 

 in the vestibulum and oesophagus, which are closed up by the peristom, may 

 be observed during the whole process. We have no means of deciding which 

 of these two statements is correct : yet we rather incline to Stein's account ; 

 for when we admit that in fission there is a separation of all the organs and 

 appendages of the body into two portions, one to each resultant being, an act 

 of stnictural development becomes necessary to reproduce the remaining por- 

 tion, so as to perfect each new animal and to assimilate it in characters to 

 the parent. This being the case, the method of development stated by Stein 

 is more consonant Avith oiu' ^dews of histogeny than that of Lachmann. 



The oblique fission of Lagenophrys vaginicola (XXX. 32, 35, 36) presents 

 several peculiarities. The line of section commences below the peristom on 

 one side, and proceeds diagonally across to the opposite, and thus gives rise to 

 an anterior lateral segment retaining all the special organs, and a posterior 

 lateral possessing nothing save its half of the elongated divided nucleus. 

 Diuing the process, the anterior half continues in the enjoyment of all its 

 functions and activity (XXX. 32), whirls its ciliary organ, and takes in food 

 by the mouth : the food, however, does not reach to the segment behind ; and 

 whatever alimentary particles might be present in this vanish, and its whole 

 contained substance becomes homogeneous and granular, the half of the 

 curved band-like nucleus extending into it. WTien the line of section is fully 

 formed. Stein remarks that the posterior lateral segment rather resembles a 

 gemma than the result of self-division, and j)roves how closely united are the 

 two processes of gemmation and of fission. 



WTien the scission is nearly complete, a contractile space appears, and, 

 either before or behind this, a curved elongated cavity, ciliated on one side 

 and produced upwards as a tube from one angle, is formed (XXX. 35), out 

 of which the rotary organ and peristom are developed. As there is no room 

 for movement, the new being lies motionless close against the old one : how- 

 ever, its contractile space acts energetically ; and the alimentary tube, filled 

 with fluid, moves upwards and downwards, and from side to side within it. At 

 length a row of cilia appear around the circumference of the body ; and now 

 two beings occupy one case, the anterior adhering by its peristom to the narrow 



