94 AN INTRODUCTION TO ZOOLOGY 



of all the others. Reproduction likewise takes place in each 

 cell. 



So far as known reproduction of only one kind occurs; this is 

 the simultaneous longitudinal division of each cell into two, four, 

 eight, and finally sixteen daughter cells. These daughter cells 

 do not separate as do the daughter cells when Chlamydomonas 

 divides, but remain fastened together by a gelatinous matrix. 

 Each cell of the mother colony thus produces a daughter colony 

 of sixteen cells. If another kind of reproduction does take place, 

 it is probably by the union of similar gametes forming a zygote 

 similar to that of Chlamydomonas. 



Pandorina morum (Fig. 45) is likewise a colonial form found in 

 fresh-water ponds. It consists of sixteen cells which are held 

 together by a gelatinous matrix, part of which is secreted by each 

 cell (I). Each cell possesses one pair of flagella and an eye spot, 

 and contains chlorophyll. It is thus enabled to carry on all of the 

 processes necessary to sustain life, to grow, and to reproduce. 



Reproduction in this species takes place in two ways. First, 

 as in Spondylomorum, each cell may divide to form two, four, 

 eight, and then sixteen daughter cells, which become a new colony 

 (Fig. 45, II). The new colonies escape from the mother colony 

 by the dissolution of the gelatinous envelope, and swim away to 

 lead a separate existence. This method of reproduction occurs 

 repeatedly, but finally conjugation is inaugurated. Each of the 

 sixteen cells of the mother colony produces by division sixteen or 

 thirty-two daughter cells. Each daughter cell develops flagella 

 and separates not only from the mother colony, but from its sister 

 cells in the daughter colony (III). This separation results from 

 a solution of not only the gelatinous envelope of the mother colony 

 but also that which holds the daughter cells together. These 

 isolated cells are known as gametes. The gametes are not all of 

 the same size, some being larger t han others. When two gametes 

 meet, they become fastened together by their anterior ends and 

 gradually fuse (IV-V). The fused cells constitute a zygote, con- 

 taining two eye spots and bearing four flagella (V). The flagella 



