PROTOZOA 



21 



contact with a female colony, it remains attached to it and breaks up 

 into single male gametes. Volvo? (which leads almost directly by its 

 method of reproduction to the higher plants and animals) is closely 

 connected with Endorina. 



In Volvox (Fig. 21) the colony appears on a higher scale of de- 

 velopment, as a division of labour takes place among the different 

 individuals. Only some individuals are capable of reproduction ; in the 

 asexual generation these individuals are the parthenogonidia (every 

 parthenogonidium produces, by continuous incomplete fission, a colony 

 which separates from the mother colony) ; in the sexual generation 

 they are gametes. Unlike the Endorina, Volwx produces, in one and 

 the same colony, male and female gametes. The female gametes are 

 simple individuals of the colony, only distinguished by their greater 





o 







0.- 



S V -s 



FIG. 21. Volvox globator. Sexual, hermaphrodite colony, after Cienkovsky and Butschli, 

 combined and somewhat diagrammatic. .S', Male gametes (spermatozoa) ; 0, female gametes (eggs). 



growth. The male gametes, on the contrary, arise in masses, by the 

 successive fission of certain individuals (cells) of the colony. From one 

 such mother-cell as many as 128 male gametes may proceed. The 

 male gametes separate, move about by means of their flagella, and 

 copulate with the female gametes. By successive division (into 2, 4, 

 8, 16, and so on) of the stationary zygotes a colony, i.e. a young Volco.i; 

 arises. 



We have here before us a true alternation of generations, 

 asexually reproducing generations alternating with sexually reproducing 

 generations. The sexual reproduction corresponds with the method of 

 reproduction of the Metazoa and higher plants. The hermaphrodite 

 Volvox (Flagellate colony) corresponds with a very simple hermaphro- 

 dite metazoon. The female gametes represent the eggs, the male 

 gametes the spermatozoa; the copulation of the female and male 

 gametes corresponds with a simple form of fertilisation of the egg by 

 means of spermatozoa. The zygote represents the fertilised egg. The 

 formation of a new Volvox colony by successive fission of the zygote 



