632 THE ANIMAL KINGDOM. 



The Hirudinea are classified as follows 



1. Rhynchobdellidae : body elongate, cylindrical, or flat, with well-marked 

 anterior as well as posterior suckers ; fore-part of the body retractile, and constitutes 

 a proboscis. Piscicola, Pontobdella, Branchellion, Clepsine, &c. 



2. Gnathobdellidae : no proboscis. Anterior end of the body more or less 

 expanded; mouth sucker-like; pharynx usually armed with three jaws; blood- 

 plasma red. Hirudo, Haemadipsa, Leptostoma, Trocheta, Aulostoma, Nephelis, &c. 



See lit. pp. 216; 218; 220; 223. 



Batrachobdella, Viguier, A. Z. Expt. viii. 1879-80. Lophobdellidae, Poirier and 

 Rochebrune, A. N. H. (5), xiv. 1884. 



Generative organs of Pontobdella, Dutilleul, C. R. 102, 1886; development in 

 Clepsine, Nusbaum, Z. A. viii. 1885. 



Development: Germ-layers in Clepsine, Whitman, Z. A. ix. 1886; Bergh, ibid. 

 Metamorphosis of Aulostoma, Bergh, Arb. Zool. Zoot. Inst. Wurzburg, vii. 1885; 

 of ' Nephelis, Id. Z. W. Z. xli. 1885. 



CLASS ROTIFERA. 



Unisegmental Vermes with a retractile trochal apparattis at the anterior 

 end of the body, and a posterior foot which is a ventral process of the body. 

 There is a single ganglion dor sally placed, a pair of nephridial ttibes, and 

 a coelome. Circulatory organs are absent. The sexes are separate, and the 

 male with rare exceptions arrested in development. Parthenogenetic (?). 



The body is protected by a cuticle secreted by an underlying layer 

 of ectodermic protoplasm with scattered nuclei, i.e. by a syncyticum. 

 This cuticle is often delicate ; gelatinous in Notommata centrura ; sometimes 

 thickened as a series of rings which gives to the body a segmented appear- 

 ance, or as a variously shaped shield or lorica protecting the body more or 

 less perfectly. A moult has been observed only in one instance (Apodoides 

 stygius\ One or two Rotifers are furnished with long spines, e.g. Triarthra; 

 and Pedalion mira has six hollow processes, terminating in a number of 

 feathered setae and containing muscles like the limbs of Arthropoda. Some 

 few Rotifera develope round themselves a gelatinous case, which they 

 inhabit permanently (Flosctdariadae) or temporarily (Philodina), the origin 

 of which is unknown. Melicerta fashions a case of pellets out of material 

 collected in a ciliated groove below the trochal apparatus, and cemented 

 together by a gland. The trochal apparatus is sometimes absent altogether, 

 e. g. Balatro, or feebly developed, e. g. Albertia. It appears to consist 

 typically of an internal prae-oral ring of long cilia, the trochus, and an 

 external ring of finer cilia, the cingulum which leads into the mouth ; the 

 former is the homologue of the prae-oral ring of cilia in the Trochosphere, 

 the latter of the adoral ciliated band, seen not in all but in many examples 

 of the same larval form. Both rings may be interrupted dorsally, and the 



