Exogenous Division in the Amoeban Rhizopods. 31 



without. In the former case it is a normal physiological 

 process originating in an inherited idiosyncrasy of the 

 organism, independently of any externally applied force ; in 

 the latter it is almost always a mere mechanical disruption of 

 the animal's body-substance, brought about entirely by forces 

 which are in nowise inherent in the organism. In short, 

 endogenous division must be regarded as a normal function of 

 the Amoeban structure, indispensable for the perpetuation of 

 its kind ; exogenous division being in reality an abnormal 

 lesion of the structure calculated to interfere with the natural 

 functions and development of the individual, just as it does 

 in cases of injury accidentally inflicted on more highly organ- 

 ized creatures. 



My attention having been lately redirected to this subject 

 by the receipt of an important paper " On the Biology and 

 Physiology of the Protozoa " * kindly sent me some months 

 ago by Prof. Gruber, of the University of Freiburg (a trans- 

 lation of which, by Mr. W. S. Dallas, F.L.S., appeared in 

 last month's issue of the ' Annals'), 1 am in hopes that the 

 present observations may serve not only to confirm Dr. 

 Gruber's views, but to furnish some new facts in relation to 

 that portion of his paper which deals briefly but specially with 

 " The Significance of the Nucleus in the Regeneration " 

 of the Amoebce • the main portion of the paper being devoted 

 to an exposition of the physiology of the Stentors and 

 other Infusoria proper. 



But although I fully accept Dr. Gruber's conclusions con- 

 cerning the paramount importance of the nucleus as a repro- 

 ductive organ, and, as far back as 1865, showed my recog- 

 nition of the fact by dividing the Bhizopods into three distinct 

 orders based entirely/ on the absence or presence of the nucleus 

 and contractile vesicle, I regret that I cannot accept the infer- 

 ence that division as noticeable in Amceha when produced 

 by artificial means, such as pressure or the dissecting-needle 

 and ophthalmic scalpel, and when conducted under conditions 

 so palpably unfavourable to the preservation of vitality in 

 the detached masses of the Amoeban body as imprisonment 

 on an ordinary microscopical slide, can be regarded as 

 affording a trustworthy parallel with what takes place when 

 an accidentally-divided Amoeba is living in the midst of its 

 natural habitat. Indeed it appears to me to be extremely 

 doubtful if exogenous division, in my sense of the term, takes 

 place at all under strictly normal conditions. When it occurs 

 whilst the organism is under observation on a slide, it is only 



* ' Berichte der naturforsclienden Gesellschaft zu Freiburg i. B.,' 

 Band i. (1886) Heft 2. 



