88 



PRINCIPLES OF ANIMAL BIOLOGY 



With regard to differentiation the simplest colonial form of the 

 scries is Gonium, of which there are two species, G. sociale with only 

 four cells and G. pedorale with 16 cells arranged in the form of a plate. 



Fig. 56. — Eudorina elegans Ehrenberg. A, adult colony, X 475; B, daughter colony 

 produced Ijy division of one of the cells of A, X 7.30; C—E, development of spermatozoa 

 from a mother cell; F, spermatozoa. (From West after Goehcl.) 



The cells of these species are so arranged that all their fiagella protrude 



from the same side of the jelly mass. The inclusion of Gonium pedorale, 



a flat plate, among spheroid colonies would be open 

 to question if it were not for the fact that the cells 

 of the young colony are not arranged in a plate but 

 in a rounded mass formed by division in three planes. 

 By a subsequent rearrangement of the cells they 

 come to lie in a plane. The adult colonj^ of Gonium 

 pedorale and Gonium sociale are showm in Fig. 58. 

 Pandorina morum forms the next step in the series. 

 A colony of Pandorina (Fig. 59) consists of a com- 

 pact group of 8 to 32 cells, the usual number being 

 16, arranged in the form of a small sphere. The 

 whole is embedded in a secreted jelly-mass to which 

 each cell contributes. Since the cells are in contact 

 their sides are flattened. Each cell resembles a little 

 pyramid whose apex is at or near the center of the 

 sphere. A slight step in advance of Pandorina is 

 presented by Eudorina elegans. A colony of Eudo- 

 rina (Fig. 56) consists of 32 cells situated rather far 

 apart and near the surface of a nearly spherical mass 



of jelly. In each of these forms (Gonium, Pandorina, Eudorina) the 



cells of a colony are similar to one another. 



-cur 



Fig. 57.— Chla- 

 mydomonas, a single 

 vegetative cell. a, 

 stigma; chr, chroma- 

 tophore; g, flagellum; 

 k, nucleus; py, pyre- 

 noid ; v, vacuoles. 

 (From Hcgner after 

 Oltmanns.) 



