THE VITAL PROPERTIES OF THE CELL 287 



in the oogonium. The male cells, on the contrary (Fig. 156 F), 

 are even smaller and more motile than those already described, 

 and ha\e assumed the characteristic properties of antherozoids ; 



t? 



FIG. 150. Spermatozoids of Fucus (x 540). Egg, with adhering spermatozoids. (After 

 Strasburger, Fig. 87 6 and F.) 



they are composed almost entirely of nuclear substance, and are 

 provided with two flagella, which function as organs of locomo- 

 tion. 



The view that eggs and spermatozoids of the higher Algse are 

 derived genetically from swarm- cells, which differentiate them- 

 selves sexually in opposite directions, and gradually assume a 

 specific male and female form, is still more strongly supported by 

 the phenomena observed in the little family of Volvocinese than 

 by comparing various species of Algse. 



This family is especially interesting and important in the 

 consideration of the problem in question, since some of the various 

 species, which in their whole appearance are extremely similar 

 (Pandorina morum, Eudorina elegans, Volvox globator), exhibit 

 marked differences in their sexual cells, whilst others show no 

 difference at all, and in yet others an intermediate stage can be 

 observed. The whole relationship is so clearly demonstrated 

 that it is worth while to consider it more in detail. 



Pandorina morum, which is especially well known for as early 

 as 1869 Pringsheim (VII. 35) discovered the pairing of its 

 swarm-spores forms small colonies of about sixteen cells, which 

 are enclosed in a common gelatinous sheath (Fig. 157 JJ). Each 

 cell bears two flagella on its anterior end ; these stretch out 

 beyond the surface of the gelatinous sheath, and are used for 

 locomotion. 



During sexual reproduction each of the sixteen cells splits up 

 generally into eight portions, which after a time are set free, and 



