INFUSORIA. 



[ 344 ] 



INFUSORIA. 



tents, which is a colourless liquid, is doubt- 

 ful. Dujardin regards it as consisting of 

 water, and as existing in vacuoles similar to 

 the vacuoles or gastric cavities ; whilst Sie- 

 bold finds here a kind of rudimentary circu- 

 lation of a nutritive fluid, comparable to the 

 circulation of the blood. In certain Infu- 

 soria, as Paramecium (PL 24. fig. 56), this 

 phenomenon is observed to take place be- 

 tween a central rounded and several elon- 

 gated and radiating cavities ; and the liquid 

 contents are seen to be propelled from the 

 former into the latter, and vice versd. These 

 contractile or pulsating vesicles or spaces, 

 as they are called, never contain foreign 

 particles ; they are tolerably constant in po- 

 sition in the same species of Infusoria ; and 

 they do not rotate nor move like the gastric 

 cavities ; all which facts are opposed to the 

 notion of identity with the latter. Yet they are 

 found in some Algae, as Volvox, which would 

 negative their relation to an animal circulation. 

 Ehrenberg regarded them as seminal vesicles. 

 Another kind of circulation takes place in 

 some of the larger Infusoria. This is a rota- 

 tion of the mass of the internal substance of 

 the body, situated between the outer coat and 

 a central space occupied by a thin liquid, in 

 which the nucleus lies. It has been observed 

 in Paramecium, but only in those specimens 

 having green corpuscles imbedded in the outer 

 coat. It is best understood by comparing it 

 with the circulation in a cell of CHARA. 



Nucleus. In the substance of the bodies 

 of most of the Infusoria may be perceived a 

 solid granular-looking body, of variable form, 

 mostly rounded, elongate, or curved (PI. 23. 

 fig. 53 ; PI. 24. figs. 37. 56 ; PL 25. fig. 26), 

 sometimes branched (PL 25. fig. 25), which 

 those who regard the Infusoria as consisting 

 of simple cells, consider as a true nucleus ; 

 whilst Ehrenberg regarded it as a testis. 

 The latter it certainly is not, but it is con- 

 nected with reproduction, as stated below. 



When almost any of the Infusoria are 

 allowed to remain upon a slide until most of 

 the water has evaporated, certain rounded 

 and somewhat highly refractive globules will 

 become evident at their margins (PL 25. fig. 

 2 a) ; these consist of semifluid gelatinous 

 sarcode, and they possess a remarkable ten- 

 dency to the formation of vacuoles or cavi- 

 ties in their interior, which apparently be- 

 come filled with the 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 M. Dujardin ; which is, however, 

 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, &c., PL 24. fig. 56), and the manner 

 in which the contents in the latter instance 

 are propelled from one to the other, or 

 from the radiate to the rounded vesicles. 



The argument that structures similar to 

 those of the higher animals cannot be de- 

 tected because they are proportionately small 

 in agreement with the small size of the ani- 

 mals themselves, does not probably hold 

 good; because the elementary tissues of the 

 lower animals are generally even larger than 

 in the higher ; thus, the elementary fibrillae 

 of the muscular fibres of a fly are larger than 

 those of a horse, the difference in size of the 

 muscles depending upon the number of them 

 forming a muscle ; and in the Infusoria we 

 might expect them to be single, or in small 

 number, but still distinct. It would be well 

 to prepare some of the larger Infusoria in 

 the same manner as the muscular structure 

 is prepared to exhibit the ultimate fibrillee. 



In regard to the cell-nature of the Infu- 

 soria, such can scarcely be conceived to exist 

 in- bodies surrounded by an integument 

 which is being continually ruptured at va- 

 rious points by the admission or expulsion 

 of drops of water. Again, the existence of a 

 distinct mouth, or part at which foreign bo- 

 dies are admitted, seems inconsistent with 

 the notion of a cell. The occurrence of 

 stinging organs in the outer surface, should 

 it be confirmed, would still further oppose 

 this view. The remarkable manner, also, in 

 which the substance of the crushed bodies 

 and the ova of the Entomostraca attract and 

 are consumed by Coleps, shows evidently 

 that these animals have a distinct sense of 

 taste ; for they are not only attracted by it, 

 but they may be seen to gorge themselves 

 until they become quite altered in shape 

 from distension. If the contractile vesicles 

 are the same as the gastric cavities, it is dif- 

 ficult to understand why, when containing 

 water, they should be contractile, and when 

 containing water and foreign bodies, they 

 should not be so, and should move about. 



Propagation. Distinct sexual organs are 

 unknown in the Infusoria ; and their modes 

 of propagation resemble in many respects 

 those of plants, especially the Algae; although 

 it must be remembered that the intermediate 

 generations of some of the higher animals 

 are often developed upon the same plan. It 



