History of the Hairy-bached Animalcules. 893 



though of large size, he could not with the utmost care discern 

 it directly, though he saw a distinct rotation at the mouth. 

 It swims more rarely than it crawls. Our specimen showed, 

 in the hinder part of the thick body, a large dark egg, well 

 developed. 



This species appears to be rare; I have not myself met 

 with it, nor have I noticed any record of its occurrence since 

 the publication of Ehrenberg's observations. 



Genus II. — Oh^tonotus (fflir.). 



Posterior extremity forked ; body clothed with hair. 



Sp. 2. . 0. larus {Mull.) (PI. i. Figs. 1—3.) This is the 

 most commonly observed species of the whole family, being 

 very frequently met with among duckweed, conferva, and other 

 aquatic vegetation. It is of moderate dimensions, as compared 

 with others, ranging from 1 -400th to 1 -200th of an inch in 

 length. Its body is not quite four times as long as broad ; the 

 head is roundish or obscurely triangular, passing insensibly 

 into the thick neck which separates it from the swelling ab- 

 domen. The posterior extremity is deeply forked, the two 

 divergent toes tapering to points, which are sometimes obtuse. 

 Ehrenberg distinguishes the species by its having the hairs on 

 the hinder portion of the back longer than those on the fore 

 part ; and in this distinction I concur with him, the specimens 

 that I have seen possessing the character strongly marked, 

 sometimes excessively. These long hairs are few, and spring 

 out of a dense coat of short hair, which clothes the whole body, 

 but most thickly behind. Probably this is what M. Dujardin 

 refers to when he remarks that " looking at it in profile we 

 recognize that the back is covered with asperities from be- 

 tween which the long straight hairs spring." * No one that 

 I am aware of has remarked a curious circumstance, that the 

 sides of the head are furnished (Fig. 3) with some very long 

 slender hairs, which stand out laterally, diverging, curving* 

 slightly forward, like the whiskers of a cat. I have observed 

 the animal frequently bend and straighten them rapidly, near 

 the tips, one independently of another, with a movement very 

 different from an ordinary ciliary vibration. A strong ciliary 

 current is produced on each side, by which floating atoms are 

 drawn towards the head, and then rapidly hurled about half- 

 way down the body. Vigorous ciliary currents aro seen to 

 pass along the inferior surface of the neck : I havo not often 

 been able to define these as forming two bands, though occa- 

 sionally they are traceable, reaching nearly as far as the bottom 

 of the posterior cleft, and then turning abruptly up and run- 



* Hist. d. Infusoires, p. 570. See, however, infra, under Das. antenniger. 



