SUCTOKIA 783 



forms. And the differences between them, consisting chiefly in the 

 shape of their bodies, the disposition of their cilia, the possession of 

 other locomotive appendages, the position of the mouth, the presence 

 of a distinct anal orifice, and the like, are matters of such trivial 

 importance as compared with those leading features of their structure 

 and physiology on which we have been dwelling that it does not 

 seem desirable to attempt in this place to give any detailed account 

 of them. The life-history of the ciliate Infusoria is a subject 

 pre-eminently worthy of the attention of microscopists. who can 

 scarcely be better employed than in tracing out the sequence of its 

 phenomena with similar care and assiduity to that displayed by 

 Messrs. Dallinger and Drysdale in the study of the Monadina. ' In 

 pursuing our researches,' say these excellent observers, 'we have 

 become practically convinced of what we have theoretically assumed 

 the absolute necessity for prolonged and patient observation of 

 the same forms. Competent optical means, careful interpreta- 

 tion, close observation, and time are alone capable of solving the 

 problem.' 



Suctoria. The suctorial Infusoria constitute a well-marked 

 group, all belonging to one family, Acitiftina, the nature of which 

 has been until recently much misunderstood, chiefly on account of 

 the parasitism of their habit. They may be regarded as a sub-class 

 of the Infusoria, and be known as the Acinetaria. Like the 

 typical Monadina, they are closed cells, each having its nucleus and 

 contractile vesicle ; but instead of freely swimming through the water, 

 they attach themselves by flexible peduncles, sometimes to the stems of 

 Vot ticettinte, but also to filamentous Algse, stems of zoophytes, or to the 

 1 K idies of larger animals. Their nutriment is obtained through delicate 

 tubular extensions of the ectosarc. which act as suctorial tentacles 

 (fig 598), the free extremity of each being dilated into a little 

 knob, which flattens out into a button-like disc when it is applied 

 to a food-particle. Free-swimming Infusoria are captured by these 

 organs, of which several quickly bend over towards the one which 

 was at first touched, so as firmly to secure the prey; and when 

 several have thus attached themselves, the movements of the 

 imprisoned animal become feebler, and at last cease altogether, its 

 body being drawn nearer to that of its captor. Instead, however, 

 of being received into its interior like the prey of Actlnophrys, the 

 captured animalcule remains on the outside, but yields up its soft 

 substance to the suctorial power of its victor. As soon as the suck- 

 ing disc has worked its way through the envelope of the body to 

 which it has attached itself, a very rapid stream, indicated by the 

 granules it carries, sets along the tube, and pours itself into the 

 interior of the Acineta-body. Solid particles are not received through 

 these suctorial tentacles, so that the Aci'tiffina cannot be fed with 

 indigo or carmine; but, so far as can be ascertained by observation 

 of what goes 011 within their bodies, there is a general protoplasmic 

 ci/closis without the formation of any special digestive vesicles.' 

 The better known forms of this group aretranked under the two genera 

 Acineta and I'lido/iJn-i/a, which are chiefly distinguished by the 

 presence of a firm envelope or lorica in the former, while the body 



