350 



GENERAL HISTORY OF THE INFUSORIA. 



nerally in Colpoda CucuUulus, which he never found in process of fission 

 (XXIX. 38-47). Indeed, Ehrenberg himself never saw self-division of 

 this animalcule, although he has, on the authority and ambiguous observa- 

 tions of some of the old observers, described its occuiTence. According to 

 Stein's researches, encysting would not appear absolutely necessary ; for he 

 witnessed self-division in some specimens only contracted in a spherical form : 

 however, in others, the more numerous, a cyst was thrown around the body 

 before that process ensued. According to the general plan, the Ciliated 

 Protozoa di\ide into two ; yet there are some — and Colpoda is one of such — 

 in which the act of fission is repeated, and 4, 8, and even 16 segments and 

 upwards result. The products of fission have a certain latitude of motion 

 within their cysts, and ultimately escape by rupture. Another peculiarity 

 about Colpoda is, that the segments resulting from fission secrete individually 

 a capsule around themselves, and thus we have encysted beings enclosed 

 within a general cyst. Lastly, each young cyst has its own nucleus and 

 contractile vesicle (XXIX. 43). 



The fission of the animal when encysted appears to be the rule in Glau- 

 coma ; for example, in G. scintillans ; and Stein surmises that it is this 

 occurrence which Cohn witnessed in Chilodon uncinatus, and thought to be 

 two animalcules enclosed within a common cyst, as happens with Gregarhiw. 



The importance of fission as a means of multiplying individuals among the 

 CiHata admits of numerous striking illustrations. We may quote one given 

 by Ehrenberg, by no means an extraordinary instance. He made out that 

 a single individual of Stylonycliia Mytilus lived nine days : during the first 

 24 hours it divided into 3 ; and duiing the next space of 24 hours each of 

 these three had subdivided into two beings ; so that by self- division alone 

 this animalcule can multiply itself three or fourfold in foiu' and twenty hours, 

 and in the space of ten days be represented by a million derived beings or 

 offshoots. Another instance may be adduced from the same distinguished 

 micrographer. On the 14th of November, he divided a Paramecium Aiirelia, 

 yL-th of a line in length, into four parts, each of which he placed in a sepa- 

 rate glass. On the 17th, the glasses numbered 1 and 4 each contained an iso- 

 lated Paramecium swimming actively about. The pieces in Nos. 3 and 2 had 

 disappeared. On the 18th, there was no change. On the 19th, each animal- 

 cule presented a constriction across the middle of the body. On the 20th, 

 No. 1 had propagated 5 individuals by transverse fission, and No. 4 eight 

 such. On the 21st, no change had taken place. On the 22nd, No. 1 contained 

 6, and No. 4, 18 specimens. On the 23rd, the beings produced were too nu- 

 merous to be counted. From these notes Ehrenberg calculated, if this process 

 continued in activity for a month, 268 millions might be produced. Apart, 

 however, from these, which we may term speculative considerations, we have 

 in Ophrydium the clearest and most direct evidence of the extent to which 

 fission is carried out. On the completion of self-di\T.sion in this animal, the 

 products remain together, connected by a common gelatinous mass at their 

 base exerted by themselves. By the repetition of the process again and again, 

 through a long series, the Opliryd'ia accumulate in large greenish masses, or 

 poljT^aries, at times of the size of the fist or even of the head of a man. Now, 

 by comparing the size of the individual Ophrydia (about y^th of an inch in 

 length) with that of the masses they form, "some estimate," says Dr. Car- 

 penter {The Microscope, p. 487), " may be formed of the number included in the 

 latter ; for a cubic inch would contain nearly e'lgJit millions of them, if they were 

 closely packed ; and many times that number must exist in the larger masses, 

 even making allowance for the fact that the bodies of the animalcules are 

 separated from each other by their gelatinous cushion, and that the masses 



