PART 11. 

 A SYSTEMATIC HISTORY OF INFUSORIA 



[Note. — The several groups whose general history is treated of in the first part of this 

 work, viz. Baeillaria (p. 1), Phytozoa (p. HI), Protozoa (p. 199), and Kotatoria (p. 392), 

 being independent of each other, their respective families, genera, and species will not, for 

 the reason stated in the Preface, be described in the same order in this second part, but 

 those of the Baeillaria will be printed last. For an explanation of abbreviations, see end 

 of Contents.] 



OF THE GROUP PHYTOZOA (p. 111). 



Families: — 1. Monadina; 2. Hydromorina ; 3. Cryptomonadina ; 

 4. Volvocina; 5. Vibrionia ; 6. Astasisea. 



FAMILY 1.— MONADINA. 



(Plate XVIII. figs. 1 to 28.) 



The Monadina are among the most minute living creatures which have been 

 discovered by man. They are (according to Ehrenberg) destitute of an ali- 

 mentary canal, are iUoricated or sheU-less, and have a uniform body without 

 any appendages issuing from it, cilia not being considered as such. They 

 increase by simj)le and complete self- division into two, foiu', or more indi- 

 viduals. The uniformity or unvarying appearance in their external form (he 

 says) may be considered as one of the principal characteristics of this family ; 

 for no one of the Monadina can voluntaiily alter the shape of its body, whether 

 into a filiform, knotty, or globular figure, nor can it extend any portion of it, 

 and then contract it again. AU possess organs of locomotion, nutrition, and 

 propagation, the last of the hermaphrodite character. Some of them have a 

 rudimentary eye ; but it has never been discerned that they are furnished with 

 a vascular or circidating system, which, however, is not surprising when we 

 reflect that, should they possess it (a supposition by no means to be rejected), 

 the diameters of the tubes of this system would necessarily be of such extreme 

 minuteness as to defy investigation. None but microscopes of high magnify- 

 ing powers can display their structure ; indeed they cannot be observed 

 accurately with a less ampHfication than 500 diameters, by glasses of consi- 

 derable penetration and good defimtion. 



The apparent eye of some Monadina is used as a generic character for 

 Microglena (XVIII. 6), Phacelomonas, &c. ; but its possession does not prove 

 the existence of sensibility, although, as Ehrenberg thinks, this facidty is pre- 

 sumable from the alternate vibration and quiescence exhibited by the pro- 

 boscis when one of these beings is in a place abundantly supplied ^\ith food. 



The details given in the first part of thiswork (p. 130), of the natm-e and struc- 

 ture of the animalcidcs comprised by Ehrenberg in this family, render it unne- 



