HEPHOJDUCTION IN THE INFUSORJA. 187 



resemble certain of the higher animals. But, unlike these, 

 they do not possess special organs for copulation. What, 

 then, are the parts concerned in that act of sexual union 

 which must, of necessity, precede the fecundation of the 

 ovarian contents? To answer this question intelligibly, 

 M. Balbiaui has premised a brief account of the form of 

 the body in these animals, Avith particular reference to the 

 position of the mouth. 



" All the Infusoria may be arranged under two great 

 categories, according to the position which the mouth occu- 

 pies in these animalcules. In the one it is situate at the 

 anterior end of the body, and in the direction of its longi- 

 tudinal axis; in the other, which constitute the great ma- 

 jority, this orifice is placed excentric to that axis on one of 

 the sides of the body, and usually in its anterior moiety." 



Let us first examine the specialities which may be observed 

 in the latter case. Very frequently the entrance to the 

 alimentary canal occupies the farthest part of a longitudinal 

 furrow, traversing the whole surface of the body, one of 

 whose margins, sometimes both, is furnished with a row of 

 of cilia more or less developed, and destined to excite in 

 the water a whirlpool which may bring particles of food 

 towards the commencement of the digestive cavity. A 

 number of modifications, varying with the species, mark 

 the shape of this depression. Thus, in Stylonychia, Oxy- 

 tricha, and most other genera of the same family, as also 

 in several Paramecina, it takes on the form of a trian- 

 gular demi-canal, much spread out in its anterior portion, 

 and becoming narrower posteriorly, in the direction of the 

 mouth. In other species, as Spirostomum, Plagiotoma, 

 &c., it may be compared to a straight groove, extending from 

 the summit of the body up to the buccal orifice, into the 

 interior of which it penetrates, and describes a spiral, accom- 

 panied by the row of cilia fringing one of its margins. Be- 

 sides these principal modes of arrangement the above de- 

 pression presents a great number of intermediate on which 

 it would be useless here to dwell. I shall, however, point 

 out the peculiar position which it assumes in Vorticellina and 

 Stentor, among which, instead of being situated, as in other 

 Infusoria, longitudinally on the side of the body, and, con- 

 sequently, parallel to its axis, it is placed, on the contrary, 

 perpendicularly to the axis of the summit of the animal, and 

 constitutes the wall which limits on this side the urn- or 

 trumpet-shaped body of these latter species. This wall, in 

 fact, repeats all the essential characters of the buccal groove 

 in the Oxytrichina and other Infusoria, with this difference, 



