240 Descri2)tioa of the Plates. 



m. Longitudinal muscles, the action of wliich^ as also of the 

 circular muscleSj giving the body its annulated appear- 

 ance, is counteracted by the elasticity of the chitinous 

 integuments. 



For a description of the Hj/dafma Senta, see Cohn^ Zeitschriffc fiir 



Wiss. Zool., 1B55; or Huxley, Med. Times and Gazette, July 



26, 1856. 

 For the anatomy and relationships of the Rotifera generally, see 



Huxley, Trans. Micros. Soc, 1853, 1-19; Moxon, Linn. Soc. 



Trans., xxiv., 1864, p. 459 ; Pritehard, ' Infusoria/ 4th ed., pp. 



468, 656. 



Figure 6. 



Figure of Turbellarian Worm (Dendrocoelum Nausicaa), after O. Schmidt, Zeitschrift 

 fur Wissenschaftliche Zoologie, Bd. xi., Taf. ii., fig. i. 



This figure is intended to show, firstly, the general external 

 appearance of this Turbellarian, which bears a strong resemblance 

 to that of the common Dendrocoelum lacteum, which is found 

 abundantly in the streams and ditches of the south of England, 

 especially in masses of the American weed {Anacliaris Ahinastrum) ; 

 and secondly, the peculiarities of the digestive system, whence the 

 Dendrocoelous sub-order of Turbellarians takes its name. The 

 cilia which cover the whole of the bodies of these worms, and from 

 which the order takes its name, as also the nervous system, and 

 the complicated organs of generation, with the exception of the 

 intromittent organ with its capsule, and an organ of obscure func- 

 tion but of similar outer form to the male organ, have been omitted 

 in this figure. 



a. Muscular pharynx, communicating with the mouth, which 

 lies a little posteriorly to the middle of the body. The 

 pharynx is in this species so long as to require to be thrown 

 into convolutions when retracted into its sheath, and it 

 attains thus a deceptive similarity to the proboscis of the 

 Nemertines or Rhynchocaelous Turbellarians. Probably in 

 no true Turbellarian does the mouth open quite terminally 

 at the cephalic extremity of the mouth, and the organ which 



