660 SYSTEMATIC HISTORY OF THE INFUSORIA. 



crdaria, and Notommata have required to be subdivided, part being thi'own 

 into one subdivision and part into another. Objects which present such close 

 resemblance as to be capable of arrangement in one generic group can scarcely 

 be so diverse as to justify their separation into different families. The de- 

 tachment of the fifth section from the fourth, merely because its individuals 

 are furnished mth short pedal forceps, would furnish a precedent for classi- 

 fying birds and quadrupeds according as they have long tails or short ones. 

 These reasons have led us to retain the classification of Ehrenberg for the 

 present, since the advantages afforded by the two newer systems do not seem 

 sufiiciently great to justify our abandoning the general plan followed in the 

 previous editions of this work. At the same time we are fully ahve to its 

 imperfections, both in its principles and details. Leydig's objection to Ehren- 

 berg's employment of the term lorica is a substantial one, since it is stretching 

 the term beyond what is admissible, to apply it to the delicate investing 

 membranes of Floscularia and StepTianoceros, or to the gelatinous envelope of 

 Conochilus. Consequently, though for reasons already advanced we retain 

 the subdivisions of the Prussian microscopist, we extend his definitions of his 

 third series of groups : instead of defining them as" loricated,''^ and "illoricated," 

 we would describe them as '^loricated, or usually provided with a hard 

 investing layer," and '' illoricated, or unprovided with a hardened investing 

 layer." 



Leydig's objection, that such animals as Ehrenberg indicates by the terms 

 Polytrocha and Zygotrocha have no existence, is ill founded. There is no 

 question that the ciliated lobes of the head are divisible and distinct in a 

 large number of species ; and being so, they become as good characteristics of 

 families as do Leydig's long or short pincers to the foot. 



FAMILY I.— ICHTHYDINA. 



Kotatoria with a single continuous rotary organ, not cut or lobed at the 

 margin ; destitute of lorica or indm-ated integument. In Ftijgura and Qh- 

 nopliora the wheel-like organ is in the form of a cii^le, and is an instrument 

 of locomotion. In the other genera it is long eUiptical, and on the ventral 

 surface. Chcetonohis and Ichthydmm have each a forked foot-like process, 

 and the rest of the genera a simple one. A long simple alimentaiy canal, 

 with a long oesophagus, apparently without teeth, occiu's in Ohcetonotm and 

 Ichihydium. Glenophora has a short oesophagus, with two single teeth ; and 

 Ptygura an elongated stomach and three teeth. Glands are seen only in 

 Chcetonotus and Ptygura. No caeca exist in any of the genera. The male 

 reproductive organs, not hitherto discovered ; those of the female consist, in 

 Ptygura and Iclithydium, of a large ovarium containing one or more developed 

 ova. The two red eyes seen in GlenopJiora are supposed by some to indicate 

 the existence of a nervous system as yet undiscovered. 



Ehrenberg's classification of this family will be found in p. 478 of the 

 General History. It is probably the weakest which Ehrenberg has esta- 

 blished, being admitted neither by Dujardin nor Leydig. Dujardin does not 

 recognize the genus Glenophora, neither does Siebold, whilst Leydig rejects 

 both it and Ptygura, regarding them as immature forms of some other 

 species. Ptygura especially, the latter writer suggests, may be the young 

 MeUcerta rhigens ; but this idea Professor AVilliamson's obsei-vations have 

 shown to be erroneous ; consequently the genus must be retained until its 

 immature condition is better established than at present. Dujardin com- 

 prehends Ptygura in his family of Mclicertiens, whilst he rejects Ichthydium 



