PROTOZOA OF nERTFOUDSHIRE. 119 



fuiu'tion of the contractile vesicle is excretory, in gettinj? rid of tlie 

 large amount of water taken in Avith the incepted food -material. 

 He says : " It is conspicuously evident, when watching the feeding- 

 process of a VorticeUa, or other highly-organised Infusorian, that 

 each spheroidal pellet, or isolated fragment of incepted pabulum, is 

 inclosed within an equal, or even more extensive mass of water, 

 and which liquid, without some special outlet for its discharge, 

 would soon accumulate to an extent incompatible with the well- 

 heing of the animal." It is very easy to understand that the 

 immense quantity of water thus brought into the endoplasm, and 

 circulating by means of the tributary canaliculi through every part, 

 re-oxygenises the plasma, and thus fulfils the role of a rudimentary 

 respiration ; the contractile vesicle being the reservoir into which 

 the fluid debouches after thus circulating through the body, and 

 fi'om which it is discharged after accumulating. 



Brief mention must be made of another structure to be discerned 

 in the endoplasm, which is assumed to be the elemental factor of all 

 infusorial life. It is called the nucleus or endoplad. In its initial 

 phase it has a simple spherical form, but in the more highly- 

 organised forms it is more elongated ; it looks like a string of 

 beads in the Stcntor family. 



In the section Pantostomata, which we are now studying, an oral 

 aperture or mouth does not exist. Recent investigation has demon- 

 strated that an anal aperture, or cytopyge, exists in the majority of 

 the species, although this organ is rarely to be seen except during 

 the passage of rejectamenta ; in the present section it is situated 

 posteriorly. 



Perhaps there is nothing more wonderful or interesting in the 

 study of the Infusoria than their reproductive phenomena, which 

 may be divided into three processes : Binary Bivision, or splitting 

 into two parts ; Gemmation, or budding ; and Sporular MaUiplica- 

 tion, or breaking into infinitesimal spores. 



The earliest recognized, and by far the most ordinary method, is 

 that of binary division. In the majority of cases this fission takes 

 a transverse direction. A groove or constriction makes its appearance 

 in the centre of the body, which becomes deeper and deeper until 

 the two bodies become entirely separated, each half moving away 

 as an independent animalcule. 



This method is characteristic of the Vorticellidae, and by means 

 of this the tree-like colony-stocks are built up. 



As the infusorial body, with all its various modifications, has 

 only the structure and functions of a simple cell, so this special 

 mode of reproduction is merely a reflex of that exhibited by all 

 cellular elements of higher structures. In all cellular structures, 

 from the simplest to the most complex, increase of growth and 

 size is always effected by binary or duplicative division of the cells 

 of which it is composed. 



By this method, Epistylis grandis produces colonial aggregations 

 many feet in extent. The Spongida, or sponges, are now regarded 

 by some writers as being merely modified aggregations of flagellate 



