VOLVOX 



183 



become arranged to form a daughter colony which swims around 

 in the interior of the mother colony. Sometimes several of the 

 daughter colonies may be developed, and they finally escape 

 by the rupture of the parent structure. The sexual cells, or 

 gametes, are of two sorts : (1) large female cells, which are called 

 eggs because they are without cilia and consequently never 

 motile, and (2) small male cells, or sperms, of peculiar form, 

 with two cilia, and consequently very actively motile. The eggs 



FIG. 178. Volvox globator, a colonial form of the Volvocacece 



A, mature colony, with four daughter colonies developing in its interior; B, sec- 

 tion of the edge of the colony, showing three vegetative cells and a developing 

 egg ; C, a , packet of sperms within the parent cell and a single sperm very 

 much magnified at the side; D, an egg surrounded by a swarm of sperms; 

 E, an oospore with heavy protective wall. C, after Cohn. 



(Fig. 178, B, D), formed by the enlargement of vegetative cells, 

 escape into the interior of the colony as naked spherical proto- 

 plasts. The sperms (Fig. 178, C) are developed in great num- 

 bers within enlarged vegetative cells. They are also set free 

 within the parent colony and gather about the eggs in swarms 

 (Fig. 178, D). Finally, a single sperm fuses with each egg, which 

 is then said to be fertilized. The fertilized egg immediately 

 forms a cell wall about itself and passes through a period of 

 rest as an oospore (Sec. 200). 



