252 MANUAL OF ZOOLOGY. 



AFFINITIES OF ROTIFERA. In their external appearance the 

 Rotifera approximate closely to the Infusoria, but the organ- 

 isation of the former presents a very striking advance when 

 compared with that of the latter. Thus, in the Infusoria there 

 is no differentiated body-cavity, bounded by distinct walls, and 

 the alimentary canal is imperfect, the digestive sac simply 

 opening inferiorly into the diffluent sarcode of the centre of 

 the body. Further, there are no traces of a nervous system, 

 and the contractile vesicles, if looked upon as representing the 

 water-vascular system, are a very rudimentary form of this 

 apparatus. In the Rotifera, on the other hand, the alimentary 

 canal forms a complete tube, having an oral and an anal aper- 

 ture, and not communicating with the surrounding perivisceral 

 cavity ; and there is a well-developed nervous system, and a 

 highly complex water-vascular system. A real affinity is found 

 to subsist, however, between the Rotifera and the Planarida ; 

 both possessing external cilia, a nervous system, and a well- 

 developed water-vascular apparatus, the characters of which 

 are not dissimilar in the two groups. In the Planarida, how- 

 ever, the sexes are united in the same individual, and there is 

 no anal aperture ; whereas in the Rotifera the sexes are dis- 

 tinct, and there is a distinct anus. To the true Arthropoda, 

 as already pointed out, the Rotifera show some points of 

 affinity, but these are hardly sufficiently numerous or decided 

 to warrant the removal of the group from the Scoledda to beside 

 the higher Annulosa. 



LITERATURE. 



GENERAL WORKS. 



1. "Entozoa: an Introduction to the Study of Helminthology. " T. 



Spencer Cobbold. 1864. 



2. " Entozoa : being a Supplement to the Introduction to the Study of 



Helminthology." T. Spencer Cobbold. 1869. 



3. "The Internal Parasites of our Domesticated Animals." T. Spencer 



Cobbold. 1874. 



4. "Parasites." T. Spencer Cobbold. 1879. 



5. "Die Menschlichen Parasiten." Rudolf Leuckart. 1863 and 1876. 



6. "On Animal and Vegetable Parasites of the Human Body." Kiichen- 



meister. Translated from the German by Dr E. Lankester. 1857. 



7. " Catalogue of the Species of Entozoa, or Intestinal Worms, contained 



in the Collection of the British Museum." W. Baird. 1853. 



8. "The Science and Practice of Medicine." W. Aitken. (Vol. ii. con- 



tains an excellent summary of the chief facts concerning the Entozoa 

 of Man. ) 



9. " Synopsis of Entozoa." Leidy. 1856. 



10. " Elements of Medical Zoology." Moquin-Tandon. Translated from 

 the French by Dr Hulme. 1861. 



