130 GENERAL HISTORY OF THE INFUSORIA, 



many Phytozoa render themselves so by the evident masses or accumulations 

 they form. The dust-hke stratum frequently noticeable on the surface of 

 water, or at the sheltered margins of ponds, is often composed of various 

 genera, such as Euglena, ChJorogonium, Pandoirina, and Gonium, more or 

 less intermingled with other Infusorial beings, such as ciliated Protozoa, 

 Desmidieae, and Diatomese. The stratum at times assumes the appearance 

 of a slimy film, at others of a frothy scum. 



Moreover, the variable affinity of different genera for light will cause a film 

 at one part of a pond to differ in its composition from that at another, when 

 the degree of exposure of the two is different. Eurther, there may be a 

 transition of colour, by the changing phase and attendant change of hue of 

 these organisms, or by the effects of the sun's heat and hght at noonday, 

 and of the darkness of night. Hence a pond which may be coloured green in 

 the warmth of the day, when the sun's influence brings the Phytozoa to the 

 surface and causes their rapid development, may in the morning and evening 

 become quite clear, o^^dng to their settlement at the bottom. 



Of the modes of obtaining the Phytozoa for examination there is nothing- 

 special to record, except it be a plan mentioned by Cohn in his account of 

 Stephanosjihcera {A. N. H. 1852, x. p. 405) : — "At their stations," writes this 

 observer, " the Step'hanospli(xra-^)\\.eYe^ occur mingled with Chlamydococcus, 

 but by no means in the abundance requisite for the investigation ; and although 

 green clouds do collect at certain points in the water wholly composed of our 

 VolvocinecB, it is difficult to extract sufficient of them for examination, since 

 they immediately start apart when touched. I succeeded in overcoming this 

 inconvenience by a simple means, so as to bring thousands of these elegant 

 organisms on to the object-holder at any moment. I took, namely, a flat 

 bottle with a short narrow neck, and nearly fUled it with the water contain- 

 ing Stephanosph<x.r(B, stopped it with a cork, and then laid it horizontally, so 

 that the cork partly dipped in the water. In a few hours almost all the 

 StepTianosphcerce in the water collected on the cork, which was covered with 

 a green coat, composed exclusively of the revolving spheres, while the rest of 

 the water in the bottle contained only Chlamydococcus, and scarcely any 

 Steplianosphcera ; so that when I wished to examine them I had only to take 

 out the cork, and a drop of the water adhering to it furnished me with aU the 

 stages of development of our organism simultaneously in very large numbers. 

 After a short time the StephanospJicerce had again assembled on the cork." 



For a more satisfactory elucidation of the Phytozoa, of their structure and 

 physiological action, it is necessary to enter into more detail ; and since there 

 is so much structural diversity among the several groups or tribes, this more 

 lengthened account must be given of each tribe separately. And first — 



FAMILY I.— OF THE MONADINA. 



(Plate XYIII. 1-28.) 



In the systematic portion of his great work, in 1838, Ehrenberg instituted 

 the follo^ving genera of Monadina, viz. Monas, Uvella, Polytoma, Microglena, 

 Phacelomonas, Glenomorum, Doxococcus, Chilomonas, and Bodo. Subsequent 

 researches led him to add the genus Chloraster, and to remove Polytoma in 

 order to unite it mth a newly discovered genus, named by him Spondylomorum, 

 in a distinct family, the ffydromorina. This family, however, deserves no 

 special consideration, but wiU fall within the compass of our general remarks 

 on the Monadina, as will also the genus Anthojphysa, in accordance with the 

 results of Cohn's researches. (See Part IL, Systematic History of Monadina.) 



