100 THE OCEAN WORLD. 
by the rupture of the globule. These are each furnished with one or 
two flagelliform filaments, which, by their agitation, determine the 
movement by rotation of the mass. 
The common Volvox, V. globator (Figs. 32 and 33), is found in 
great abundance, during summer and even in the depth of winter, in 
lakes and ponds of fresh water. It consists of green or brownish-yellow 
globules about the thirtieth part of an inch, formed of monadiform 
beings scattered round a gelatinous and diaphanous spherical disc, 
each furnished with a flagelliform filament and with a reddish in- 
terior point, which Ehrenberg took for an eye. Leuwenhoek first 
observed this Volvox in marshy waters. This eminent naturalist has 
left a very interesting account of his observations on these micro- 
scopic creatures, displaying an amount of patience and address which 
cannot be too much admired ; his observations were made with a 
simple lens, which he constructed himself. In one hand he held his 
instrament—which was very coarse if we compare it to the more 
perfect and infinitely more powerful instruments now in use—whilst, 
in the other hand, he carried to it the glass tube full of water which 
contained the objects under observation. ‘The microscopes of 
Leuwenhoek,” says Dujardin, “were bi-convex lenses of the very 
smallest size, mounted in a silver frame-work. He made a collection 
of twenty-six, which he bequeathed to the Royal Society of London. 
These instruments, subject to all the inconveniences of a maximum of 
spherical aberration and a total want of stability, were only fit for 
use in the hands of Leuwenhoek himself, who had acquired, by his 
labours of twenty years, habits of observation which compensated, in 
great part, for the want of perfection in his instruments.” We now 
come to those forms considered as belonging to the 
FLAGELLATE INFUSORIA. 
The Jfonads are infusorial animalcules which make an early 
appearance in vegetable infusions. They constitute a family that are 
destitute of any tegumentary covering. The substance of their 
bodies can shorten itself, or draw itself out more or less ; their whip- 
like filaments serve as organs of locomotion. Their organisation is 
extremely simple ; their whip-like filaments are so fine as to be 
scarcely perceptible, their length is sometimes double and even 
quadruple the length of the animal itself. 
The Lens Monad (Fig. 34) is a species which is frequently met 
with in vegetable and animal infusions. The older microscopists had 
it indicated under the form of a globule, moving in a slow and 
