434 Illinois State Laboratory of Natural History. 



Volvox they are actually connected by protoplasmic processes. 

 (4) The beginnings of histological differentiation are also 

 evident in the cells composing the so-called colony. In 

 Eudorina, according to Carter ('58), the cells are differen- 

 tiated into male and female in definite regions, the male cells 

 developing from the anterior quartet and the remainder 

 becoming female ; in Volvox sexual and asexual reproduction 

 alike are limited to a few of the cells ; and in Pleodorina the 

 asexual process is confined to the posterior hemisphere. The 

 cells of the organism are thus histologically and functionally 

 differentiated in this particular in these higher genera. 

 Although the degree of differentiation is slight, it is neverthe- 

 less appreciable. (5) In the matter of locomotion the 

 activities of the individual cells of the organism are not 

 independent of each other but are correlated, the flagella 

 acting together to produce rotation, its reversal, or its cessa- 

 tion. The predominance of the direction in the higher genera 

 plainly exhibits the phenomenon of correlated locomotor 

 activities of the constituent cells. 



The facts above cited emphasize the desirability of regard- 

 ing each of these so-called colonial flagellates of the sub- 

 family VolvocincB as a unit, with an organization of its own, 

 and not as a colony, that is. an aggregation of independent 

 and similar cells associated merely as a result of descent from 

 a common parental cell, the form being a matter of chance 

 or circumstance. The group of cells as a whole, and not 

 each of the constituent cells, is the unit of descent, of form, 

 and of function, and the word colony can be applied to it 

 only by the license of usage and as a matter of convenience. 



Reference has been made frequently in the preceding pages 

 to the prevalence of colonies whose symmetry has been dis- 

 turbed by loss of cells. In most instances only the empty 

 secondary sheath remains, giving no clue to the cause of the 

 loss of its contents. In collections made in Phelps Lake, 

 Havana, 111., in August, 1896, however, colonies were often 

 found which were parasitized by one of the Sj)orochytriace<z, 

 which upon examination proves to be Danyrardia mamillata, 

 described by Schroder ('98) as a parasite of Pandorina 



