PEOFESSOE W. C. WILLIAMSON ON VOLVOX GLOBATOE. 335 



On comparing one of the cells of a young Volvoa^, prior 

 to the shrinking of its cell-contents, with those of many of 

 the Alg9B, we find the very closest resemblance existing 

 between them. On advancing a stage further, when the 

 cells have become ciliated, and the organism capable of 

 locomotion, we have a condition which is common among 

 the zoospores of the Confervse. In the development and 

 temporary existence of the large green granule {Fig. 4 b), we 

 have another point of resemblance to the Confervse. It 

 exists under precisely similar conditions in many of the 

 Algae. If we watch the development of the various species 

 of Coccochloris in their earliest stages, we shall invariably 

 detect the appearance of a single corresponding granule in 

 the interior of each cell. It exists in the young states of 

 most of the DesmidiacecB, and is especially obvious in the 

 species of Cosmarium, Euastrum, and Arihrodesmus. It is 

 also a curious fact, that when two new segments are pro- 

 duced between two others of older growth (a common 

 phenomenon amongst the Desmidiace(s\ each of the new 

 portions exhibits the characteristic granule. 



In some stages of its development amongst the Desmi- 

 diacecB, this granule appears to contain an abundance of 

 starch. Hence we may regard it as the analogue of the 

 similar granules, of which a few exist in the very young cells 

 of the Zygenemata, and into the composition of which starch 

 enters largely. The number of these granules in each cell 

 varies considerably. In Coccochloris, and other fresh-water 

 Ulvaceous plants, I have never seen more than one. In the 

 young states of the Arihrodesmus ^ Euastrum, and Cosma- 

 rium, we have invariably one, and occasionally two, in each 

 segment. Mr. Ralfs considers each individual of these 

 genera as consisting of but one cell, with symmetrical con- 

 strictions ; and consequently we have as many granules for 

 each cell as there are segments. I have just examined a 

 young example of Cosmxirium margaritiferum, which con- 



