ROTIFERA. 



409 



same faculty of resuscitation after desiccation. 

 On account of the slow movement of Macro- 

 biotuSy they have been called Tardigrada ; an 

 objectionable term, because applied to a family 

 higher up in the scale of development. On 

 account of their habit of crawling, and not 

 swimming as the great mass of Rotifers, Du- 

 jardin names them Systolides marchcurs. They 

 are interesting as connecting the Rotifers, not 

 only with the Annelida, but also, through their 

 four pair of feet, with the higher forms of the 

 Articulata, and on the other side with the 

 Helminthida. Ehrenberg regards Macro- 

 biotus not as a Rotifer, but as an animal re- 

 lated to Lerntsa. This epizoon and its con- 

 geners have undoubtedly more affinity with 

 the articulate than wMi the molluscous tribes ; 

 and the relation of the Tardigrades with the 

 Rotifers establishes for that family a more 

 decided tendency towards the articulate groups 

 than any other. 



Although the organisation of the Rotifera 

 is included in too small a space to permit of 

 dissection, the transparency of their integu- 

 ments is so great as to permit of an easy ex- 

 amination of their internal organs. From 

 the previous descriptions of the families of 

 this order, it will be seen that their organis- 

 ation is very complicated, and that their size 

 is by no means the measure of their position 

 in the animal scale. 



Tegumentary system. The Rotifers are 

 all covered with a resisting tegument, more 

 or less flexible, and which is the last part of 

 the body to decompose. The composition of 

 this tunic, although possessing various degrees 

 of density, appears to be entirely organic ; and 

 the absence of siliceous or calcareous matter 

 will account for these animals being never 

 seen in a fossilised state. The investing 

 membrane is open in front, to allow of the 

 contact of the fleshy interior with the water 

 in which the creatures live. There is, also, 

 an anal orifice. In those species in which this 

 membrane is not hardened, so as to form a 

 shield, it is capable of being folded by the 

 action of the muscles, and possesses a number 

 of false articulations. The anterior part, to 

 which are attached the vibratile ciliae consti- 

 tuting the rotatory organ, is capable of being 

 retracted into, or thrust out from, the rest of 

 the body. All the parts of the body retract 

 within the skin into a kind of globule, when 

 the animal is removed from the water. The 

 tegument has attached to it various .organs, 

 as the claws in Emydimn, the cirrhi, or fins, 

 of Polyar/hra, and the elongated setae of Tri- 

 arthra (fig. 297.), the teeth in the dense tegu- 

 ment, or lorica, of Brachioncea (fig. 296. g,g). 

 The tail, or foot, must be regarded as an 

 elongation of the tegument. It varies much 

 in size and length. Sometimes it consists of 

 a single styliform seta, as in Triarthra longi- 

 seta (fig. 297.) ; in the genera Monura and 

 Monostyla it is styliform, but is also articu- 

 lated. In some of the species of the genus 

 Anuraea there is no tail at all. In most in- 

 stances the tail is forked, as in Hydatina, 

 Euchlanis, Philodina, Rotifer, Brachionus, $c. 



(figs. 293296.). Sometimes the tail is di- 

 vided from the point of its origin with the tegu- 



Fig. 297. 



Triarthra longiseta. (After Ehrenberg'). 



a, a, muscular fibres ; b, contractile vesicle ; c, r, 

 intestinal glands. 



ment of the body, as in Notommata longiseta 

 (fig. 298.) and in Hydallna senta (fig.293.). 

 More frequently a portion intervenes between 

 the body and the terminal processes. This 

 is soft and movable in every part in Brachio- 

 nus pala (Jig. 296.) ; forms a series of sheaths 



