224 



PRACTICAL ZOOLOGY 



Sporulation is apparently a rare process of multiplication 

 in Ameba. First, the pseudopodia are drawn in and the animal 

 becomes spherical. By successive divisions of the nucleus from 

 five hundred to six hundred daughter nuclei are produced. Cell 

 walls then appear, dividing the Ameba into as many cells as there 

 are nuclei. These cells break away and 

 grow into Ameba in about three weeks. 



Euglena. — A third type of Protozoon 

 that may occur abundantly in laboratory 

 cultures is the little greenish, spindle- 

 shaped animal known as Euglena (Fig. 

 134). The principal interests Euglena has 

 for us are its methods of locomotion and nu- 

 trition. At the anterior end of Euglena 

 there is a long, whip-like filament which 

 bends to and fro, drawing the animal along. 

 This filament is called flagellum. 



For its nutrition, Euglena probably does 

 not ingest solid particles by means of its 

 mouth (Fig. 134, m) and gullet, but manu- 

 factures its own food by the aid of the 

 green substance (chlorophyll) contained in 

 it (chr). As in plants, this chlorophyll is 

 able, in the presence of light, to break 

 down the carbon dioxide, thus setting free 

 the oxygen, and to unite the carbon with 

 water, forming a substance allied to starch, 

 called paramylum (am). This mode of 

 nutrition is known as holophytic. Euglena 

 differs from most animals in its method of nutrition, since the 

 majority of them ingest solid particles and are said to be holo- 

 zoic. 



Other Fresh-water Protozoa. — Paramecium, Ameba, and Eu- 

 glena are only three of the more common Protozoa to be found in 

 fresh water. A great many others will be seen on the slides 



Fig. 134. — Euglena. 



am, pyrenoid ; chr, 

 chromatophores ; cv, 

 contractile vacuoles; e, 

 stigma, or eyespot ; m, 

 mouth ; n, nucleus ; r, 

 reservoir. (From 

 Bourne.) 



