OF THE TARDIGEADA. 713 



Genus TETRASIPHON (Ehr.).— We have not met with the detail of the 

 generic characters, but they may be gathered from the description of the 

 following species : — 



Tetrasiphon Hydrocora. — Very 

 large, hyaline, with two prominent tu- 

 bular occipital organs, and other two 

 near the termination of the back ; pan- 

 creatic glands fom', globose; jaws bi- 



dentate, with the oblique rotary organ 

 of Pleurotrocha. Foot with slender, long 

 and acute toes; eye occipital. Length 

 1-36" and upwards. Berlin. 



Genus DIPODINA. — Characters unknown. 



DiPODiNA Artiscon (Ehr.) (^lentioned 

 in Reports of Zoology, Ray Society). — 

 Approaches Notommata, but differs by a 



particular constriction of its tarsal nip- 

 pers (toes). Found by Ehrenberg at 

 Wismar, on the Baltic. 



The genus Polych^dtus (XXXVIII. 31, 32) of Perty is supposed by Leydig 

 to be a Crustacean. Ctphonautes is also regarded by the same observer as 

 dubious ; whilst, as we have already observed, he regards Ptygura and Gleno- 

 phora as undeveloped forms of other species. 



OF THE GROUP TARDIGRADA. 



The creatures thus named are introduced here as a group, inasmuch as they 

 cannot be included amongst the Rotatoria. Some remarks on their organiza- 

 tion will be found in Part I. (p. 482) of this work ; and here I shall introduce 

 fm-ther particulars, chiefly derived from the first edition of this work (1834), 

 p. 182, and from Dujardin's Hist, des Tnfusoires, p. 661. They have oblong 

 bodies, contracted into a baU; furnished with four pairs of short feet or 

 mammilliform processes, each terminated by simple or double hooked claws ; 

 mouth very narrow, siphon- shaped ; with an internal maxillary apparatus 

 composed of two lateral moveable pieces, and of a strong muscular oesophageal 

 bulb, furnished with horn-like dental articulated processes. 



The Tardigrada stand on the one side between the Rotatoria (Systolides, 

 Duj.) and the Helminthidas, and on the other between the AnneKda and 

 Ai'achnida. 



These creatures are usually found attached to aquatic plants which float 

 upon still water. I first obtained them from ponds in the Regent's Park. 

 By placing some water with, the plants in a common white hand-basin, and 

 shaking the vegetation, they are detached and fall to the bottom of the basin, 

 from whence they are readily taken. They are generally met with, in com- 

 pany with the larger kinds of Rotatoria, in moss. They are very sluggish in 

 their movements, and are commonly knoT?VTi under the name of " little water- 

 bears." Under the polarizing microscope the manducatory apparatus exhibits 

 the same appearance as horn. They are capable of resuscitation after being 

 dried. They vaiy in length from 1-20" to 1-50". 



M. Doyere, in an elaborate Memoir in the ' Annales des Sciences,' has 

 divided the Tardigrada into four genera : — 



Genus EMYDITIM. — Body oval, anterior part narrow, and terminating in 

 a pointed mouth, near to which, on each side, are flesh-like papillje. Feet 



