238 Prof. H. Fol 07i the Family Tintinnodea. 



The body (PL XVII. figs. 2 and 4) is, in general terms, 

 conical, terminated above by a broad disk, and produced below 

 into a contractile appendage which is longer or shorter accord- 

 ing to the species. Energetic as are the contractions of this 

 sort of peduncle, it nevertheless does not present that trans- 

 verse striation, recalling the texture of the striped muscles, 

 which characterizes the peduncle of the Vorticellce. Clapar^de 

 and Lachmann (VII. p. 195) have clearly recognized this fact, 

 which helps to establish the distinction between the Tintinni 

 and the Vorticellce. Stein has observed that, when the animal 

 detaches itself from its test, the peduncle enters into the body 

 and becomes confounded with it — a proof that it consists of 

 sarcode with no special differentiation. 



The superior discoidal extremity or peristome, when the 

 animal is in a state of perfect extension, Ib placed a little 

 obliquely with relation to the aperture of the test. This posi- 

 tion, and the long cilia which garnish it, give it a great re- 

 semblance to the disk of the Vorticellce. Nevertheless this 

 similitude is only apparent, as Claparfede and Lachmann 

 have well remarked. In fact, the mouth, instead of being 

 placed at the outer margin of the disk, as in the Vorticellce^ 

 is situated in its interior, and often even near its centre. The 

 disk itself, instead of being flat or slightly convex, as is the 

 case in the Vorticellina, is hollowed out like a saucer ; and 

 the vibratile cilia, instead of forming a single row round the 

 margin of the disk, are implanted in great numbers and in 

 several lines over the greater part of the surface. 



The arrangement of these vibratile cilia is exceedingly 

 curious and interesting, and deserves to fix our attention tlie 

 more because it has not been described by any of the authors 

 who have busied themselves with the Tintinni. 



The whole margin of the disk is occupied by long and strong 

 motor cilia, which strike the water vigorously and give tlie 

 animal an exceedingly rapid rectilinear movement of transla- 

 tion. All authors speak of this unruly natation, and of the 

 rapidity with which the animal traverses the field of the ob- 

 jective, and they make it an excuse for any thing that may 

 be imperfect in their descriptions. 



I have spoken of a rectilinear movement. It is thus, in 

 fact, that the animals habitually swim ; but they can readily 

 deviate from the direct line when they have to avoid an ob- 

 stacle. Moreover the animal is constantly turning upon itself 

 during its progress, which is therefore comparable to that of a 

 rifle-ball. 



As soon as these great motor cilia commence their action, 

 they present the so-called phenomenon of rotation in a high 



