IKFUSOEIA. 



[ 418 ] 



INFUSORIA. 



to be inadmissible; and in some instances, 

 at least (PL 30. fig. 19), the reddish-violet 

 colour is real, and arises from the presence 

 of solution of the colouring-matter of Oscil- 

 lutorice, which is often different by reflected 

 and transmitted light. 



The particles of solid matter forming the 

 food of the Infusoria, are usually drawn to 

 the oral orifice by tlie action of the cilia. 

 The manner in which Actinophnjs takes its 

 food is described under that head ; but, from 

 Lachmann's observations, the rays of Aci- 

 netu ai'e hollow suctorial organs. 



In many of the organisms included among 

 the Infusoria, the food-particles are ingested 

 at any parts of the entire surface, or at 

 certain parts only, no mouth being present. 

 Circtilaf.ing si/stetn. — On closely watching 

 almost any of the Infusoria, minute, mostly 

 rounded, clear spots are seen in the sub- 

 stance of the body, disappearing and reap- 

 pearing at pretty regular intervals. These 

 are the contractile vesicles ; they are of var- 

 able size, but about that of the gastric 

 cavities. The nature of their contents, 

 which is a colourless liquid, is doubtful. 

 Dujardin regards it as consisting of water, 

 and as existing in vacuoles similar to the 

 vacuoles or gastric cavities ; whilst Siebold 

 and others find here a kind of rudimentary 

 circulation of a nutritive fluid, comparable 

 to the circulation of the blood. In certain 

 Infusoria, as Pararnecimn (PI. 31. fig. 56), 

 this phenomenon is observed to take place 

 between a central rounded and several 

 elongated and radiating cavities, and the 

 liquid contents are seen to be propelled 

 from the former into the latter, and vice 

 versa. These contractile or pulsating vesi- 

 cles or spaces, as they are called, never 

 contain foreign particles ; they are tolerably 

 constant in position in the same species of 

 Infusoria ; and they do not rotate nor move 

 like the gastric cavities ; all of which facts 

 are opposed to the notion of identity with 

 the latter. The contracting vesicles of 

 some species open externally through a 

 canal ; and in others a long internal vessel is 

 continuous with them. They are found in 

 some Algaj, as Volvox, Chlamidomonas, 

 Gonivm, Si/ncrypta, as in Dinuhnjon and 

 Eiic/lena, wbich would negative their relation 

 to an animal circulation. Kent, however, 

 considers the presence or absence of the 

 contractile vesicle a ready means of dis- 

 tinguishing unicellular animal from vege- 

 table organisms. Lieberkiihn and Lach- 

 mann describe distinct vascular branches 



arising from the contractile vesicles, not 

 penetrating the internal sarcode of the body. 

 Another kind of circulation takes place 

 in some of the larger Infusoria. This is a 

 rotation of the mass of the internal sub- 

 stance of the body. It has been observed 

 in Parnniecium, but only in those specimens 

 having green coi-puscles imbedded in the 

 outer coat. 



When almost any of the Infusoria are 

 allowed to remain upon a slide until most 

 of the water has evaporated, roimded and 

 somewhat highly retractive globules will 

 become evident at their margins (PI. 32. 

 fig. 2 a) ; these consist of the semifluid 

 gelatinous sarcode forming the interior of 

 the body, and they possess a remarkable 

 tendency to the formation of vacuoles or 

 cavities within them, which apparently be- 

 come filled with tbe surrounding water. 

 This fact is perhaps the strongest in favour 

 of the formation of the gastric cavities and 

 contractile vesicles within the body of the 

 living animals in the same manner as sup- 

 posed by Dujardin ; which, however, is 

 opposed, in the case of the contractile vesi- 

 cles, by their tolerably constantly uniform 

 position, and especially their remarkable 

 form (as in the stellate vesicles of Parame- 

 cium itc, PI. 31. tig. 56), and the manner 

 in which the contents in tlie latter instance 

 are propelled from one to the other, or from 

 the radiate to the rounded vesicles. 



Nucleus. — In tlie substance of the bodies 

 of most of the Infusoria may be perceived a 

 solid granidar-looking body, of variable 

 form, mostlv rounded, elonsrate, or curved 

 (PI. 30. tig."5o ; PL 31. figs.^37, 56; PL 32. 

 fig. 26), sometimes branched (PL 32. fig. 25), 

 which those who regard the Infusoria as 

 consisting of simple cells consider a true 

 nucleus, whilst Ehrenberg regarded it as a 

 testis. 



Nucleolus. —This is usually a small body, 

 in or upon the nucleus, and with a high 

 refractive power. 



Propagation and reproduction. — The In- 

 fusoria increase in numbers by the following 

 methods: — 1. Fission or self-divLsion. This 

 occurs in (o) the perfect form of the animal- 

 cule, and (h) after it has become encysted. 

 2. Gemmation or budding. 3. Conjugation. 



1. Fission or self-division. — {a.) Sponta- 

 neous division is either longitudinal (PL 32. 

 fig. 37) or transverse (fig. 3S). In both, the 

 nucleus undergoes division, as well ns the 

 body. In the longitudinal division the pro- 

 cess commences at one end of the body, 



