MICROSCOPIC FORMS OF ANIMAL LIFE. 39 



to the equatorial furrow. They pass into a quiescent condition, subsid- 

 ing 'towards the bottom of the water; and the loricated forms appear to 

 throw off their envelopes. But whether these changes are preparatory 

 to any process of conjugation, is not known. Some of the Peridinia are 

 found in sea- water; but the most remarkable marine forms of the cilio- 

 flagellate group belong to the genus Ceratium (Fig. 301), in which the 

 cuirass extends itself into long horny appendages. In the Ceratium 

 tripos (1), there are three of its appendages; two of them curved, pro- 

 ceeding from the anterior portion of the cuirass, and the third, which is 

 straight or nearly so, from its posterior portion. They are all more or 

 less jagged or spinous. In Ceratium furca (2), the two anterior horns 

 are prolonged straight forwards, one o*f them being always longer than 

 the other; whilst the posterior is prolonged straight backwards. The 

 anterior and posterior halves of the cuirass are separated by a ciliated 

 furrow, from one point of which the flagellum arises; and at the origin of 

 this is a deep depression, into which the flagellum may be completely 

 and suddenly withdrawn. Whether this is, or is not, a true mouth lead- 

 ing into the cell-cavity, has not yet been ascertained. The Author has 

 found the Ceratium tripos extremely abundant in Lamlash Bay, Arran; 

 where it constitutes a principal article of the food of the Comatulce that 

 inhabit its bottom. 1 



433. Suctoria. The suctorial Infusoria constitute a well-marked 

 oup, all belonging to one family, Acinetina, the nature of which 

 been until recently much misunderstood, chiefly on account of the 

 parasitism of their habit. 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 pedun- 

 cles, sometimes to the stems of Vorticellince, but also to filamentous 

 Algae, stems of Zoophytes, or the bodies of larger amimals. Their nutri- 

 ment is obtained through delicate tubular extensions of the ectosarc, 

 which act as suctorial tentacles (Fig. 302) ; the free extremity of each 

 being dilated into a little knob, which flattens out into a button-like 

 disk 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 Actinophrys ( 399), the captured Animalcule 

 remains on the outside; but yields up its soft substance to the suctorial 

 power of its victor. As soon as the sucking disk 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 Acinetina 

 cannot be fed with indigo or carmine; but, so far as can be ascertained 

 by observation of what goes on within their bodies, there is a general pro- 

 toplasmic cyclosis, without the formation of any special ' digestive vesi- 

 cles.' The ordinary forms of this group are ranked under the two genera 

 Acineta and Podophrya; which are chiefly distinguished by the presence 

 of a firm envelope or lor lea in the former, while the body of the latter is 



1 See Allman in "Quart. Micr. Journ." Vol. iii. (1855), p. 24; and H. James- 

 Clark in "Ann. Nat. Hist.," Ser. 3, Vol. xviii. (1866), p. 429. 



