VARIATION IN THE DESMIDIER. 401 
The moving corpuscles in the apical locellus varied in number 
from three to nine, and were by no means constant in number 
at the two ends of the same individual. Out of sixty specimens 
observed, four possessed three moving corpuscles at the end, one 
possessed four, eleven possessed five, nine possessed six, twenty- 
nine possessed seven, three possessed eight, and three possessed 
nine. In some examples one large corpuscle was observed among 
an aggregation of small ones. 
Tue apical locellus of the genus Closterium is nothing more 
nor less than a special terminal vacuole containing moving 
corpuscles, aud although it varies considerably, it is nevertheless 
utilized in part as a generic distinction (compare the differences 
between the genera Closterium and Koya). It is a diagnostic 
feature of the genus Closterium, and is often the sole means of 
determining the correct position of small species of this genus 
which closely approach Lihaphidium, a genus of Palmellaces in 
which moving corpuscles are absent *. 
If a gathering containing a number of living Desmids be kept 
growing fur some time in a small glass vessel, it frequently 
happens that many of the specimens develop numbers of small 
moving granules in all parts of the cell. A gathering from 
Birkhouse Moor Tarn, Helvellyn, which contained a quantity of 
Pleurotenium coronatum, Rabenh., was kept growing in this 
manner for some time, and most of the specimens of this 
species became much vacuolated, Generally there were from 
Tour to six large vacuoles in each semicell, although some were 
noticed in which over twenty were present, and in the majority 
of these vacuoles a large number of moving corpuscles made 
their appearance. The latter were precisely similar to those 
present in the apical vacuoles of Pleurotenium; but were 
certainly different from the moving corpuscles present in the 
apical vacuoles of Closterium. I have noted the occurrence of 
the same phenomenon in many species of the genera Penium, 
Cosmarium, Kuastrum, Micrasterias, and Staurastrum. It would 
seem, therefore, that these moving corpuscles can be developed 
in any vacuole in the plant if the latter be placed under suitable 
conditions f. They move freely in the fluid vacuole, and always 
collect towards its base as a small, incessantly moving mass. 
* Cfr. W. Archer in Quart. Journ. Mier. Science, ii. 1862, pp. 257-8; West 
& G. S. West in Journ. Roy. Micr. Soc, 1897, p. 501. 
t Moving corpuscles of a nature similar to those found in Desmids have 
been noticed to arise in the vacuoles in the midst of the cell-contents of 
Jthaphidium polymorphum var. mirabile, 
