Zoology, S91 



excited by this most singular and beautiful phenomenon, 

 than presently the body of the animal, which had been quite 

 transparent, and bearing much resemblance, in aspect, to 

 some of the marine Rhizostomae, becomes dotted with a num- 

 ber of distinctly circumscribed circular spots, of a dark blue 

 colour, exactly corresponding to that of the moving particles 

 of indigo. In some species, particularly those which are pro- 

 vided with an annular contraction or neck (such as the Ro- 

 tifer vulgaris), separating the head from the body, the 

 particles of indigo can be traced in a continuous line in their 

 progress from the mouth to these internal cavities. Dr. Eh- 

 renberg used a microscope possessing a power of 800, made 

 by Chevalier of Paris ; but a power of from 300 to 400 he 

 found sufficient in most cases. For the purposes of measure- 

 ment he used a glass micrometer, constructed by Dollond, 

 which gives directly the ten thousandth part of an inch, and 

 permits of a much smaller quantity being correctly estimated, 

 as it contains the astonishing number of 400 equal parts dis- 

 tinctly cut in glass within the space of half a line. By means 

 of a micrometer screw, which has since been constructed by 

 Pistor of Berlin, he has been enabled to measure one forty- 

 eight thousandth of an inch, or one four thousandth of a line ; 

 a degree of minuteness which is never necessary in actual 

 practice. 



By the above infusory mode of rendering the animalcules 

 obvious, and by such a microscope and micrometer to explore 

 their structure and functions, Ehrenberg has demonstrated - 

 the existence of a digestive system in all Mliller's genera 

 of the Infusoria. The ciliae, which vary in number in differ- 

 ent species, seem to be the principal agents by which they 

 excite those currents which are so beautiful under the micro- 

 scope, and which have the effect of bringing the nutritive 

 particles infused into the water into contact with their mouths. 

 The mouth merits the notice of the systematologist ; from the 

 very precise characters which he can draw from thence for 

 his subordinate divisions. An oesophagus belongs only to 

 those animalcules which possess a notable contraction between 

 the mouth and the stomach. Of the last-named organ (sto- 

 mach) some species have several ; the Monas termo has four, 

 and other species more ; the stomach varies in form also, in 

 different species. The alimentary canal presents, as in other 

 classes of the animal kingdom, the utmost variety, in respect 

 to form, situation, and degree of complication : the anus, also, 

 in its figure and situation, exhibits much variety. 



In the muscular system of these beings, Ehrenberg has 



c c 4 



