VOLVOX 49 



sphere. In such a colony some individual cells are commonly 

 specialized to carry on the reproductive function while all of 

 the remaining cells (somatic cells) are similar. 



3. These colonies live in ponds and pools where they swim 

 about freely by the action of the flagella with which the somatic 

 cells are provided, progressing with a smooth rolling motion. 

 Ordinarily in preserved material used for study these flagella 

 are not distinguishable. 



4. There are a number of different species of Volvox. 

 These differ among themselves in details of structure as well as 

 in methods of reproduction. The material selected for this study 

 belongs to the species Volvox weismannia. In this species there 

 are two different methods of reproduction involving three differ- 

 ent types of individuals ; these are male colonies and two differ- 

 ent kinds of female colonies. 



5. The simplest and most characteristic method of repro- 

 duction is found in the parthenogenetic female colonies. In 

 these, some of the cells become set apart as reproductive cells 

 and are called parthenogenetic macrogametes. Arising in the 

 colony wall, they increase in size until they are shoved into the 

 interior of the colony. ]\Iacrogametes of this sort are capable 

 of undergoing development directly without being fertilized. 

 Each gamete, by repeated divisions, forms a group of cells which 

 become arranged as a small sphere within the parent colony. 

 Only by rupture or disintegration of the wall of the parent col- 

 ony are these young colonies liberated. This method of partheno- 

 genetic reproduction continues as long as conditions are favor- 

 able. 



6. At certain times the young colonies instead of producing 

 parthenogenetic gametes develop into true sexual individuals. 

 Thus there are formed male colonies which develop only micro- 

 gametes or male cells and sexual female colonies which produce 

 only sexual m-acrogametes. In these true sexual individuals 

 neither type of the reproductive cells is capable of undergoing 

 reproduction independently, for fertilization is necessary. When 

 fully formed the microgametes leave the male colony and pene- 



