and on their Specific Differences. 3 



Development. — The daughter consists of an enlargement of 

 one of the peripheral cells (PI. I. fig. 11 a), which thus projects 

 into the interior of the parent ; and as it enlarges, the chloro- 

 phyll and protoplasm together are seen to form an areolar struc- 

 ture around the internal periphery of the cells (fig. 4)_, which 

 goes on increasing in size, and the starch-cells and chlorophyll 

 increasing in number and quantity respectively, until a sudden 

 re-arrangement of the gonimic contents takes place, and the 

 whole is transformed into a globe of peripheral cells. (Here is the 

 great difference between this and the following species : contrast 

 figs. 4 and 6 c.) Synchronously with this, the cilia are pro- 

 duced ; the peripheral cells secrete a mucus around themselves 

 which hardens into a thin pellicle, leaving two distinct channels 

 for each pair of cilia ; the pellicle thus hardening, the daughter 

 separates itself from the cell-wall of the peripheral cell (the im- 

 mediate parent or bud), and begins to rotate; after which, 

 the peripheral cells of the parent waste and perish, and the cap- 

 sules of the daughters, which now also contain the grand- 

 daughters or third family, becoming deciduous at the same time 

 (for these capsules are but a part of the parent), the whole 

 structure breaks down, and the*young family, including the 

 grand-daughters, which now become " daughters,^' thus escapes. 

 Hence the young Volvoces only contain one generation * (PI. I. 

 fig. 3). 



Fecundation. — Sometimes, instead of the eight daughters pro- 

 ducing eight grand- daughters, and thus passing into the com- 

 mon form above described, two, three, and not unfrequently all 

 of the eight daughters may present an enlargement of thirty to 

 fifty of their peripheral cells, indiscriminately scattered over 

 the posterior three-fourths of their spheres respectively (fig. 7). 

 These cells, which are twice or thrice the size of the rest, and of 

 a light yellowish-green colour while the daughters remain within 

 the parent, become still more enlarged and of a deep dark-green 

 colour a short time after they have been liberated ; they also 

 then become surrounded by a thickened capsule, which appears 

 to be slightly wavy in its outline, and are, in short, the spores. 

 Thus we see that the daughter here is the alternating form, 



* Professor Williamson considers the mucus which forms the peUicle, 

 and ultimately becomes the cell-wall, to be secreted by the yo'.mg peri- 

 pheral cells after the development of the cilia has commenced (/. c. p. 54); 

 and I can see no other more reasonable way of accouotirg for the forma- 

 tion of the holes in the cell-wall for the passage of the cilia than this. I 

 incline to the theory which views the primordial protoplasm or utricle as 

 the organ, and the cellulose or wall with which ii becomes covered the 

 product; and that the protoplasm may was,te away by age or want of 

 nourishment, as it may also increase by the latter, but does not become 

 converted into cellulose. 



1* 



