562 



COLLEGE ZOOLOGY 



Spondylomorum 



Produces no 

 gametes 



Chiamydomonas 



Produces gametes 

 alike in size 



All reproduce 

 asexually by 

 fission 



Oo 



Pandorina 



Produces gametes 

 unlike in size 



Female colony 

 of eggs 



Eudorina 

 Figure 401. Evolution of sex in the flagellates. 



Bundle of 

 sperms 



Produces gametes 

 unlike in size 



is characteristic of female colonies. In male 

 colonies, each cell divides to form 16 or 32 

 small cells (sperms). These fuse in pairs 

 with the large cells (eggs) in the female 

 colony to form zygotes. This species pro- 

 duces sharply distinguished male and female 

 gametes. 



Volvox globator 



Volvox globator (Fig. 22, p. 48) repre- 

 sents the final stage in the series. The thou- 

 sands (one species, 50,000) of asexual cells 

 in a colony are united by protoplasmic 

 strands; physiologic continuity is thus estab- 

 lished between the cells, a condition not 

 found in the colonies previously described. 



If a single cell from the colony is cut out 

 and isolated from its neighbors, it will round 

 off like a tear-drop and swim about by means 

 of its two flagella. In this state it resembles 

 Chiamydomonas, but after a time the 

 isolated cell dies. Most of the cells of the 

 colony contain an eyespot, chloroplasts, con- 

 tractile vacuoles, and two flagella; these are 

 called "body" or somatic cells. The produc- 

 tion of daughter colonies is accomplished by 

 special reproductive cells which are set 

 aside for this purpose. 



The asexual method of reproduction is as 

 follows: certain cells of the colony become 

 larger than others and lose their flagella; they 

 increase in size, and each divides by longi- 



