138 GENEEAL HISTORY OF THE INFUSORIA. 



exist, either between the two filaments, or at the side of their points of issue 

 from the membrane. 



" During the swarming-state, a division of the substance of the body goes on 

 uninterruptedly at all hours of the day. The different stages of this process 

 follow one another with greater or less rapidity in proportion as the conditions 

 of nutrition are more or less favourable. Soon after the commencement of fer- 

 mentation in an infusion, the rate of increase attains its maximum ; it then 

 diminishes as the fermentation ceases, the offspring at the same time undergo- 

 ing a diminution of size. 



"The commencement of the process of division is indicated by the uniform 

 distribution of the granular substance. A constriction of the substance then 

 takes place, usually commencing on one side ; by this the body is divided 

 into two parts, which are still enclosed in the iminjured investing membrane. 

 Simultaneously with, or perhaps before the completion of this bisection, the 

 nucleus also divides (fig. 3). Although no constriction of the nucleus was 

 ever noticed, nothing certainly was observed to contradict the supposition 

 that the second nucleus was produced in this manner. The two halves then 

 become constricted from their sui'faces of contact, in such a manner that the 

 constriction of one half crosses that of the other at right angles (fig. 4). To 

 every depression thus produced on the one side there is a corresponding ele- 

 vation of the other. The quadrisection (figs. 9, 12) then takes place suddenly 

 as if by cutting, and mthout any appearance of a circular constriction, each por- 

 tion containing its jn'oper nucleus. The divisions now acquire an oval form, 

 and arrange themselves in such a manner that the ends of the posterior pair, 

 which are turned towards the middle, alternate with those of the anterior 

 pair in the same place (fig. 12). In very favourable circumstances (as for in- 

 stance at the commencement of fermentation), a third division into eight 

 parts takes place, each division being still furnished vi^th a nucleus. As a 

 general rale, however, the young individuals acquii^e filaments soon after the 

 quadrisection, and move about in various directions within the investing mem- 

 brane, until this biu^sts and the young, which are exactly like the mother 

 except in their smaller size, are set free. In favourable circumstances the 

 empty membrane remains vrith the two filaments. After the division of the 

 substance into four or eight parts, the investing membrane is always visible 

 without the employment of any reagents. This has not escaped Ehrenberg 

 (loc. cit. and tab. i. xxxii.) ; he explains the appearance as a consequence of a 

 superficial constriction. The filaments of the parent always appear to be con- 

 nected only with one of the young individuals, although this is less distin- 

 guishable in the present mode of di\dsion than in that about to be described. 

 " In this the quadrisection takes place in another manner. After bisection, 

 the two portions shift their position in such a manner that the surfaces of 

 contact form a distinct angle with their original position. If this change of 

 position be but trifling, the quadiisection goes forward nearly in the manner 

 just described, and the arrangement of the developed young only differs as far 

 as is rendered necessary by this change of position ffigs. 9, 12). But if it be 

 more considerable, the new surfaces of division run parallel to each other and 

 nearly perpendicular to the surfaces of contact of the two halves. The posi- 

 tion of the young individuals is then completely different from that seen in 

 the preceding case ; all four lie parallel to each other, with their longitudinal 

 axis oblique as regards the axis of the whole (fig. 10). 



" This difference may perhaps be explained as follows : — Each portion has 

 a tendency to acquire an oval form, so that soon after the bisection the ante- 

 rior portion extends itself posteriorly, and the posterior towards the front. 

 When sufficient time has not elapsed for the one dimension to predominate over 



