206 ROTIFERA 



the body is only formed in a very young state. In M. janus 

 and M. pilula it is increased by the successive deposition of ovoid 

 faecal pellets on to the rim. In M, ringens (Fig. 116) and M. coni- 

 fera pellets are formed of the excess of the food particles brought 

 to the disc by the ciliary current ; they are carried through the 

 gutters on either side of the projecting ventral lip or " chin " 

 into the ciliated glandular cup on that side of the head. Here, 

 as they revolve, they are cemented together into a pellet which 

 is spheroidal in the former species, cylindro-conoidal with a basal 

 hollow like a rifle-bullet in the latter. After a pellet is com- 

 pleted the animal stoops down and deposits it on the edge of the 

 tube. This may easily be verified by furnishing a young 

 Melicerta with water containing solid particles of carmine. M. 

 tubicolaria forms a thick tube which is laminated, the laminae 

 being directed upwards and outwards, and having diatom shells, 

 etc., between the layers. In this case we have observed that the 

 faeces are pellucid, and sometimes are so ejected as to lie in a 

 sheet against the funnel-shaped mouth of the tube, and we are 

 inclined to believe that the tube itself is formed altogether in 

 this way. A similar process probably occurs in Oecistes crystal- 

 linus and Oe. umbella. 



The muscles are simple elongated fibres, usually having near 

 the middle a mass of granular protoplasm containing a nucleus ; 

 they may be smooth or striated. The principal muscles of the 

 body are conspicuously striated in many active free-swimming 

 forms (Pedalion, Synchaeta, Pterodina, Triarthra). 



The muscles of the body-wall are transverse and longitudinal. 

 They are best seen in Bdelloida. The principal muscles of the 

 body-cavity are longitudinal ; the most conspicuous and constant 

 are the retractors of the disc and of the foot, protraction of these 

 organs being usually accomplished by the contraction of the 

 transverse muscles. Special muscles effect the vigorous spring- 

 ing of the Triarthridae and Scirtopoda ; in the former group the 

 muscles only raise the spines, and their elastic recoil is the 

 actual mechanism of progression; but in the latter (Fig. 117) 

 special flexor muscles of the limbs are the effective agents of the 

 leaping movements. 



Movements. The Eotifera vary very greatly in their move- 

 ments. The cilia of the disc, and especially of the trochus, are the 

 principal organs of prehension of food, and also of swimming when 



