44 NATURAL HISTORY 



With an achromatic microscope of a power of 500, they 

 form a most beautiful object, and various indentations and 

 markings may be detected on the surface of each globule, 

 which are worthy of investigation, as we know so little 

 about their structure. The diameter of the clusters varies 

 from 1 -600th to l-1500th of an inch: when arranged in 

 a globular mass they resemble the Volvox socialis (see 

 figure 15), of which I imagine they are only a variety. 



I have found them very abundant during the month of 

 September, on the surface of ponds, covered with a 

 brownish green film. When a drop of the water is 

 placed upon the stage-glass of the microscope, the upper 

 surface of it should be carefully examined before it is 

 covered with mica or glass, as I have found them inva- 

 riably to float on the water. 



35. Volvox morum. The mulberry Volvox. — This group 

 of animalcules differs from the former species in the 

 shape of the cluster, which is of a globular form, like 

 the fruit of the mulberry-tree, and the whole inclosed 

 in a transparent membranous envelope. The individual 

 globules, in which may sometimes be observed a slight 

 motion, are usually of a bright sea-green colour, while 

 the envelope which surrounds them is clear and pellucid, 

 like glass. The cluster swims slowly, rotating as it pro- 

 gresses. They are found, during the latter months of 

 the year, at the surface of ponds, covered with vegeta- 

 tion. Figures 16 and 17 represent two clusters of the 

 mulberry Volvox, highly magnified : in the larger ani- 

 malcule the internal cluster has separated into several 



