IOO 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 

 instrument 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 Monads 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 



