METHOD OF OBTAINING INrUSORIA, XTC. 383 



vulgaris may be found abundantly in the Isle of Dogs, in 

 ditches near the bank of the Thames, also in some of the 

 ponds on the Hippodrome, at Notting-hill. The Nitella grows 

 in ponds at Totteridge and Hendon, whilst the Hydrocharis 

 occurs in almost every ditch, and may be known by its flat 

 leaf, somewhat like that of a large species of duckweed, floating 

 on the surface of the water. The Tradescantia and Pentstemon, 

 as well as the groundsel, are common in flower gardens, but 

 the Vallisneria is principally cultivated by the microscopist ; 

 small roots of this plant may, however, be obtained of Mr. 

 Topping, and of some nurserymen. 



CHAPTER XVII. 



METHODS OF PKOCURING INFUSORT AND OTHER 

 ANIMALCULES. 



The term Infusoria was given by the older microscopists to 

 beings which, previous to their discovery by magnifying 

 powers, had been concealed from observation by the minute- 

 ness of their size. They were first detected in water contain- 

 ing vegetable matter, such as hay and grass in a state of 

 decomposition ; it was then supposed that they were peculiar 

 to infusions of a certain kind, hence their name. The cele- 

 brated Ehrenberg, who has devoted himself so entirely to 

 their structure and classification, has divided them into two 

 orders, Polygastria and Botifera ; the first being named from 

 their having many stomachs, and the last from their being 

 provided with vibratile organs resembling wheels. Amongst 

 the most remarkable of the Polygastria may be included 

 the following genera, viz., Monas^ Gonium, Volvox, Vibrio, 

 Navicula, Stentor, and Vorticella; whilst amongst the latter 

 may be named the Floscularia, Stephanoceros, Brachionus, 

 and Rotifer. 



Localities. — The ordinary forms of Infusoria are to be met 



