the Distinctive Characters in Amoeba. . 145 



former has been absent, the segment remained comparatively- 

 torpid and motionless, whilst the segment provided with this 

 organ moved away energetically as soon as the separation was 

 complete*. Under these circumstances it has yet to be deter- 

 mined whether the contractile vesicle at any time originates 

 spontaneously, or is invariably an integral part of the organism.. 

 Judging from its presence in full activity in the minute vivi- 

 parously produced Amosbce, the latter conclusion seems to me 

 most probable. But, I need hardly say, the point is one that 

 demands a great deal of careful investigation before it can be 

 regarded as settled. 



Mr. Carter {' Annals,^ 2nd series, vol. xviii. p. 129) observes, 

 in allusion to the occasional plurality of the contractile vesicles 

 in Chilodon cucullulus and the Rhizopoda generally [loo. cit. 

 p. 130), that "the synuses of this system the sarcode of 

 Amoeba not only seem to burst into each other and into the 

 vesicula, but, when the latter has contracted, another sinus, par- 

 tially dilated and situated near the border, may be seen to swell 

 out and contract after the same fashion before the reappearance 

 of the vesicula,^' — a figure (plate 7. fig. 81 a a) being appended 

 in which two contractile vesicles, in a partially distended state, 

 are represented on opposite mai-gins of the body of A. quadri- 

 lineata, and described in the explanatory text (p. 248) as being 

 " about to discharge themselves independently of the large, 

 apparently normal one," which is centrally placed between them 

 at a considerable distance from the true posterior extremity of 

 the body. 



In describing the contractile vesicle of A. villosa in the 

 ' Annals ' for April last (p. 289), I mentioned that it sometimes 

 presented a reticulated appearance. I have repeatedly seen the 

 same appearances since then, and have no doubt now that each 

 contractile vesicle is able to project from its wall supplementary 

 vesicles at points answering to the reticulations or, as I now 

 regard them, villi. But, whilst it is quite possible to conceive 

 that the contractility of the wall of the supplementary vesicles 

 is sufficient to enable their orifices of communication with a 

 principal one to remain closed until their complete expansion 

 takes place, or even to expand and collapse independently 

 during the apparent obliteration of the principal vesicle, it 

 appears to me that the view expressed by Mr. Carter in the 

 'Annals' for 1856 (vol. xviii. p. 129), namely, that "the sinuses 



* From the extreme difficulty of determining whether we are looking at 

 a contractile vesicle or a mere passive vacuole, I am unprepared to speak 

 positively as to the behaviour of a detached segment when apparently 

 devoid of the former of these organs — the diastolic condition being some- 

 times maintained without interruption for upwards of an hour. 



Ann. i^ Mag. N. Hist. Ser. 3. Vol. xii. 10 



