34 



THE AMERICAN NATURALIST 



[Vol. XLI 



for Volvox. It is more difficult to keep the material alive in the 

 laboratory during warm weather because, in exposing the dishes to 

 sunlight, the water is likely to become warmer than that of the 

 ponds in which Volvox lives. This difficulty might be overcome 

 by placing the dishes where they will be partly immersed in the 

 running water of a shallow aquarium, and at the same time receive 

 an abundance of sunHght. 



In case organisms that feed upon Volvox are too abundant, the 

 latter may be freed from its enemies by removing it with a pipette 

 when clustered at the Hghted side of the dish, to a dish of pond 

 water strained through bolting cloth to remove crustaceans, etc. 



Obtaining Volvox in the Sexual Stage. — Both in the fall and 

 in the spring, material in the sexual stage was obtained in abun- 

 dance merely by keeping the organisms alive in the laboratory. 

 Several aquaria should be set up, and in some of them, specimens 

 in the sexual stage will usually be found in the course of one or two 

 weeks. It was noted by Dr. H. H. Newman that they often remain 

 hidden in the ooze at the bottom of the dish. When they reach the 

 sexual stage they seem to become less motile and consequently 

 drop to the bottom. This is especially true of sperm colonies in 

 V. aureus. 



University of Michigan 

 Zoological Laboratory 



LITERATURE 



'99. Morphologisehe und biologische Studien iiber die Gattung Vol- 

 vox. Jahrb. f. wiss. BoL, vol. 20. 

 KOFOID, C. A. 



'99. Plankton Studies, etc. Bull. III. State Lab. Nat. Hist., vol. 5. 

 Meyer, Arthur. 



'96. Die Plasmaverbindungen und die Membranen von Volvox globa- 

 tor, aureus, und tertius, mit Ruckslcht auf die thierischen Zelleii. 

 Hot. Zrit. vol. 54, pp. 187-217. 



:06. ( ialvaiiotropism in Volvox. Am. Journ. Physiol, vol. 15, No. 3. 



