2 BRITISH FRESHWATER RHIZOPODA. 
Leeuwenhoek (cies 1675), with his simple lenses, 
began to examine drops of pond-water, and discovered 
some of the commoner ciliated forms. Continued 
observation by this naturalist and his contemporaries 
revealed a variety of life-forms; and for many years 
their origin, organization, and functions were matters 
of lively controversy. The theory, at first prevalent, 
of spontaneous generation, was in process of time 
abandoned ; but even so late as the time of Ehrenberg, 
one of the most assiduous, though not always most 
accurate, of observers, their unicellular structure, now 
universally conceded, was doubted. Imagination con- 
ceived what the imperfect microscopical appliances of 
the time failed to reveal, and the impression was formed 
that they were possessed of organs analogous to those 
of the Metazoa. Ehrenberg (1838) pictured them with 
many stomachs, and from that fancied character applied 
to them the title, now obsolete, of Polygastrica. 
The greater perfection and higher powers of modern 
microscopes have contributed to the elucidation of the 
structure of the Protozoa and of their life-functions. 
Structurally they are simple cells, or single corpuscles, 
of protoplasm. Siebold, Kélliker, and Max Schultze 
early demonstrated the groundlessness of Ehrenberg’s 
theory. Dujardin, together with Biitschli, Auerbach, 
Claparéde and Lachmann, Hertwig and Lesser, as well 
as our own countrymen Dr. Wallich, Mr. H. J. Carter, 
and Mr. William Archer, extended our knowledge of 
the tribe materially. More recently the physiological 
relations and classification of the Rhizopoda have been 
studied, and the results recorded, by Professor Ray 
Lankester and others, in the pages of the ‘ Encyclo- 
pedia Britannica,’ the ‘Journal of the Linnean 
Society,’ the ‘Quarterly Journal of Microscopical 
Science,’ and elsewhere. Naturalists abroad have for 
years worked unceasingly in the same field, and the 
scientific publications of Germany, Switzerland, Italy, 
and France, for more than a generation, have afforded 
evidence of the keen observation of Greeff, Gruber, 
