AN INTRODUCTION TO ZOOLOGY 



genus Culex are able to digest all stages of Plasmodium vivax, and 

 are therefore immune. On the other hand, this mosquito does 

 not digest all of the organisms of the malaria which attacks birds 

 and thus becomes infected and is the means of transmitting the 



fever from one bird to 

 another. 



Quinine is the rem- 

 edy commonly used 

 against the malarial 



a ^^ ,_ _ parasite. It acts di- 



rec tly upon the 

 younger stages of the 

 organism, causing 

 death. 



4. VOLVOX GLOBATOR 



AND ITS ALLIES 



Certain organisms 

 which lie on the 

 borderland between 

 plants and animals are 

 peculiarly favorable 



for illustrating how a 



FIG. 43. Chlamydomonas, A, single vegetative . . ,, , . , 



cell: a, stigma ; chr., chromatophor ; g ., fla- multicellular animal 



gellum; k., nucleus; />y., pyrenoid ; v., vac- llke Volwx (Fig. 46) 



uoles. B, Four daughter cells still within may have evolved 



the cell wall of the parent; C, the union f rO m a single-celled 



of two gametes; D, zygote. (From Olt- ancestort These or- 



manns.) 



ganisms belong to the 



Family Volvocaceae. They are important not only for their phy- 

 logenetic significance but also because they illustrate the evolu- 

 tion of sex. Starting with the unicellular Chlamydomonas, the 

 line of evolution passes through Spondylomorum, Pandorina, 

 Eudorina, and finally ends with Volwx (76). 



