32 



THE AMERICAN NATURALIST 



[Vol. XLI 



from the surface, and connected by very slender protoplasmic 

 strands, difficult for students to make out under the microscope. 

 Volvox glohator is monoecious: in the sexual stage both sperm 

 bundles and eggs may be found in the same colony at the same 

 time. The number of sperm bundles in a single colony is small. 

 Volvox aureus is either dioecious or monoecious proterogynous : 

 sperm and eggs are never found together in a single colony at the 

 same time, but the colony may contain one or the other exclusively. 

 However, I have found daughter colonies, some of which contained 

 bundles of sperms, others ova, within the same parent colony. 

 The number of sperm bundles in a single colony is very large. 

 SphcBrosira volvox Ehrenb. is an old name for the male colony of 

 Volvox aureus. 



Kofoid ('99) gives the following key for the determination of 

 the two species: 



Cells about 10,000 (minimum 1,500, maximum 22,000), angular with 

 stout connecting protoplasmic processes into which the chromato- 

 phore may enter. Diameter of colony about 700 fx (minimum 400, 

 maximum 1,200) ; diameter of ceil body 3-5 /i. V. glohator L. 



Cells 500-1000 (minimum 200, maximum 4,400) ; rounded, with slender 

 connecting protoplasmic processes into which the chromatophore 

 does not enter. Diameter of colony 170-180 /i; diameter of cell 

 body 5-80 [i. Volvox aureus Ehrenb. 



Klein ('99) gives illustrations of the general appearance of the 

 two species, including reproductive stages. Meyer ('96) gives 

 details of cell structure, with illustrations. 



Volvox glohator is probably a better form for laboratory work 

 than V. aureus, and can be obtained in greater abundance if 

 secured early in the spring. Hence if Volvox is to be studied in the 

 fall by large classes it is w ell to preserve this species in 4 % formalin 

 in the spring; for many purposes the preserved material, if not 

 kept too long, is as good as the living. The study of preserved 

 specimens of V. glohator can then be supplemented bv' the living 

 V. aureus. 



Keeping Volvox alive in the Lahoratory. — Terry ( :06) in experi- 

 menting on the galvanotropism of Volvox met with the usual 

 difficulty in keeping it alive in the laborator}% and concluded that 

 the organisms died of insufficient nourishment caused by improper 



