74 PROPAGATION OF INFUSORIA. PART in. 



leads into a large cavity in the gelatinous substance, 

 from whence the rudiments of an alimentary canal 

 descend. From the internal surface of the globe sarcode 

 fibres extend through the gelatinous matter, so as to 

 divide it into a number of irregular compartments, in 

 which vacuoles are often seen. They give buoyancy to 

 the animal, and enable it to rise and sink in the water, 

 but seem to disappear when the food is digested. The 

 sarcode fibres constantly change their form and position, 

 and the electric light emitted by a direct exertion of 

 nerve power, which seems to be constant to the naked 

 eye, really consists of momentary scintillations that in- 

 crease in rapidity and intensity by the dash of an oar or 

 the motion of the waves. 



The Noctiluca is propagated by spontaneous division, 

 a line appears bisecting the globe, which becomes more 

 and more constricted till the animal is like a dumb-bell ; 

 the slender thread separating the two parts is then 

 broken by their efforts to get free ; the two new creatures 

 swim off in different directions, and soon assume their 

 adult form. But in many individuals there are clear, 

 yellow globules with a well-defined nucleus, of a rich 

 reddish-brown, which are the germs of the animal. 



Most of the Infusoria multiply by continuous bisection, 

 like the unicellular Algse. The division generally begins 

 with the nucleus, and is longitudinal or across, according 

 to the form and nature of the animal, and is accom- 

 plished with such rapidity, that, by the computation of 

 Professor Ehrenberg, 268,000,000 of individuals might 

 be produced from one single animalcule of the species 

 Paramoecium in a month. The Paramoecia are repro- 

 duced too by gemmation, and, as they are male and 

 female, they are reproduced also like the higher classes. 



The Infusoria have another mode of increasing. The 

 animalcules either draw in or lose their cilia, and con- 

 sequently come to rest. The animal then assumes a 



