NOTES ON PLEODOEINA CALIFOKNICA SHAW. 



BY BERTRAM 0!. SMITH. 



On July 23, 1915, the writer found the colonial flagellate Pleodor- 

 ina californica Shaw in great abundance in a pond near White's 

 Woods, Ann Arbor, Michigan. Pleodorina was most plentiful at 

 the margin of the pond, where by pressing down the mat of vege- 

 tation hollows were formed which soon filled with water. In a 

 vial of this water held to the light, Pleodorina was barely visible 

 to the naked eye. When the material was placed in a finger bowl 

 in the laboratory, exposed to the light of a north window, the 

 specimens sought the side of the dish furthest from the light — ■ 

 a case of negative phototaxis that seems remarkable in view of the 

 behavior of Euglena and Volvox in similar circumstances. Such a 

 reaction in a chlorophyll-bearing flagellate would seem almost 

 suicidal. Specimens undergoing reproduction became less motile 

 and sank to the bottom of the dish. The material does not live 

 long in the laboratory. Ten days later, it had completely disap- 

 ])eared from the pond. The occurrence of Pleodorina has been 

 noted in California, where it was first discovered, also in Illinois, 

 Indiana and in southern France; I am not aware of any previous 

 record for Michigan. 



Pleodorina is a colonial protozoan, each specimen in the adult 

 stage consisting of typically 128 greenish bi-flagellate cells enclosed 

 in a common gelatinous envelope and loosely arranged to form a 

 hollow sphere. There is a decided difference in the size of the 

 cells on opposite sides of the colony. On one side, comprising a 

 little less than a hemisphere, the cells are quite small; these are 

 the somatic or body cells. On the other side, comprising a little 

 more than a liemisphere, the cells are much larger; these are the 

 reproductive or germ cells. The form of the colony is not exactly 

 spherical, but is usually elongated slightly in the direction of the 

 axis of radial svmmetrv ; in other words the colony has the form of 

 a prolate spheroid, with the body cells segregated about one pole. 

 Since the end composed of body cells usually precedes in locomo- 

 tion, this end may be called the anterior end and the opposite end 

 the posterior end. 



