ROTIFERA TARDIGRADA. 435 



IV. The fourth of M. Dujardin's primary orders consists of the 

 very curious tribe, first carefully investigated by M. Doyere, to 

 which the name of Tardigrada has been given, on account of the 

 slowness of their creeping movement. Their relation to the true 

 Rotifera, however, is not at all clear; and many naturalists regard 

 them as altogether distinct. They are found in the same loca- 

 lities with the Rotifers, and, like them, can be revivified after 

 desiccation ( 280) ; but they have a vermiform body, divided trans- 

 versely into five segments, of which one constitutes the head, 

 whilst each of the others bears a pair of little fleshy protube- 

 rances, furnished with four curved hooks, and much resembling 

 the pro-legs of a caterpillar. The head is entirely unpossessed 

 of ciliated lobes ; and it is only in the presence of a pair of jaws 

 somewhat resembling those of Rotifera, and in the correspon- 

 dence of their general grade of organization, that they bear any 

 structural relation to the class we have now been considering. 

 They may be pretty certainly regarded as a connecting link 

 between the Rotifera and the Worms ; but they should probably 

 be ranked on the worm side of the boundary. 



282. Notwithstanding that all the best informed Zoologists are 

 now agreed in ranking the class of Rotifera in the Articulated 

 series, yet there is still a considerable discordance of opinion as 

 to the precise part of that series in which they should stand. 

 For whilst Prof. Leydig, who has recently devoted much atten- 

 tion to the study of the class, regards them as most allied to the 

 Crustacea, and terms them " Ciliocrustaceans," Mr. Huxley, with 

 (as it seems to the Author) a clearer insight into their real nature, 

 has argued that they are more connected with the Annelida, 

 through the resemblance which they bear to the early larval 

 forms of that class (Fig. 274). Considered in this light, the Tar- 

 digrada might seem to represent a more advanced phase of the 

 same developmental history. 1 



1 In addition to the classical works of Ehrenberg and Dujardin, the following Me- 

 moirs should be consulted (besides those already referred to) by such as wish to 

 acquaint themselves with the best researches upon the Rotifera: Leydig in "Siebold 

 and Kolliker's Zeitschrift," Band VI, heft 1 ; Goss on Melicerta ringens, in " Transact, of 

 Microsc. Soc." Ser. I, vol. iii, p. 58; and "Quart. Journ. of Microsc. Sci." vol. i, p. 71 ; 

 Williamson on Melicerta ringens, Op. cit. p. 1; and Huxley on Lacinularia socialis, in 

 " Transact, of Microsc. Soc." Ser. II, vol. i, p. 1. 



