252 GENERAL HISTORY OF THE INFUSORIA. 



and a valvular structure of a very extraordinary natui'e are attributed to it. 

 We suspect, indeed, that Mr. Weston has been led into error by appearances, 

 — a supposition he will pardon us for making, since, as he himself tells us, his 

 microscopic experience is less than two years old. His account runs thus : — 

 " There appears to be no doubt about the existence of a valvular opening : I 

 have had some thousands of these animalcules under my observation, and 

 have never met mth a specimen where the valve was absent. It is best 

 distinguished when about the edge of the seeming disc, and, so far as my 

 observations go, is never still night nor day, — being slowly, but without cessa- 

 tion, as it were, protruded, occupying from 10 to 70 or 80 seconds in its 

 development, and then, like the bursting of a vesicle, rapidly and totally 

 subsiding ; for an instant it has utterly disappeared, only to be again as 

 gradually and as certainly reproduced. Should that side of the creature, 

 where the valve is placed, be tiu-ned from the observer, the effects of the 

 contraction are distinctly seen, although the valve itself is not ; for at the 

 instant of its bursting and closure, some half-a-dozen or more of the tenta- 

 cles, situated on or about it, which have been gradually thrust from their 

 normal position by the act of its protrusion, now rapidly approach each other 

 with a jerk-Hke motion, caused by the sudden biinging together of their 

 bases. 



" With -i-th of an inch objective, I have been led to imagine the valve to be 

 formed of a double layer of the external hyaloid membrane, the edges of 

 which appear to adhere to each other tenaciously, notwithstanding the 

 growing distension from within, until the force becomes so great that the 

 lips, as they may be called, suddenly separate, apparently to give vent to 

 some gaseous product ; and at this moment there is, as I have stated, enough 

 seen to induce the belief in the existence of a double lip -like valve, perhaps 

 the organ of respiratioyi.''^ 



He afterwards adds (p. 118) — " In many instances I have seen half-a- 

 dozen or more prisoners attracted to the tentacles of an individual, each gra- 

 dually absorbed ; and although thus busily occupied, no cessation of the action 

 of the valve takes place." Stein imagined the movements of the contractile 

 sac to be subservient to the reception of food ; but this supposition, as men- 

 tioned already (p. 248), is opposed to analogy, and is wanting in direct obser- 

 vation to establish it. 



Among the general contents of the body of Actinophrys, Kolliker (pp. cit. 

 p. 27) mentions some separable nuclear cells as detached by crushing from 

 the innermost portions of the animal. When isolated by pressure, they be- 

 have themselves as cells, with nucleus and nucleolus, sometimes as free 

 nuclei. " The author is, in fact, inchned to regard them as cells and nuclei, 

 Ipng in some of the interior vacuoles ; for such, and such only, are the vesi- 

 cular spaces in which they are enclosed." (XXIII. 29.) 



NucLErs. — Kolliker applied the term nucleus, very improperly, to the more 

 granular and darker central or medullary portion of the body (XXIII. 29 h), 

 and overlooked the presence of the real nucleus. However, Stein, Carter, 

 Cienkowsky, and others have determined the existence of this organ in the 

 genera Actinophrys and Podophrya. Unfortunately, some difference prevails in 

 the descriptions of this organ by the several observers, which it is most desirable 

 to have removed. Carter {A. N. H. 1856, x\iii. p. 221) represents it to be a 

 cloudy body, " discoid in shape, of a faint yellow colour, and fixed to one side 

 of a transparent capsule, which, being generally more or less larger than the 

 nucleus itself, causes the latter to appear as if suiTounded by a narrow pel- 

 lucid ring." Stein describes it in Actinophrys Sol as finely granular, band- 

 shaped, and curved, or reniform, or rounded oblong (XXIII. 1 b). Cien- 



