Natural History of the Infusoria. 325 



ance as a consequence of a superficial constriction. The fila- 

 ments of the parent always appear to be connected only with one 

 of the young individuals, although this is less distinguishable in 

 the present mode of division 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 quadrisection goes forward nearly in the manner just de- 

 scribed, and the arrangement of the developed young only differs 

 as far as is rendered necessary by this change of position (figs. 11 

 & 12). But if it be more considerable, the new surfaces of divi- 

 sion run parallel to each other and nearly perpendicular to the 

 surfaces of contact of the two halves. The position of the young 

 individuals is then completely different from that seen in the pre- 

 ceding case ; all four lie parallel to each other, with their longitu- 

 dinal axis oblique as regards the axis of the whole (figs. 9 & 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 anterior portion extends itself posteriorly, 

 and the posterior towards the front. When sufficient time has 

 not elapsed for the one dimension to predominate over the other, 

 the quadrisection takes place as in the former case ; but when, 

 on the other hand, one dimension has become predominant, the 

 division into four takes place in accordance with the same law as 

 the original division into two. 



The method of division first described is always met with in 

 the early periods of an infusion, which are most favourable to the 

 development of the creatures. Towards the end the latter mode 

 alone occurs. This phenomenon was so remarkable, that on 

 the first occasion of my examining an infusion towards the close 

 of its action, I imagined that I had at first misunderstood the 

 mode of division. 



Under certain circumstances the individuals pass to a state 

 of rest. They are then completely filled with the starch-like gra- 

 nules, so that the nucleus only appears as a reddish spot. The 

 substance of the body becomes spherical, and invests itself with a 

 membrane which is frequently of considerable thickness (fig. 7). 

 In this state I have never observed them to undergo any divi- 

 sion or any other change, and when dried the cysts still retain 

 their contents. When clear water is poured over them they do 

 not return to life, but would probably do so in a fermenting 

 infusion. 



The mode in which the swarming individuals arrive at this 

 state of repose appears to be as follows. The filaments are gra- 

 dually shortened, their substance collecting at the free extremity 



