376 MR. G. 8. WEST ON 
l. The structure of the cell-contents is one of the most constant 
features exhibited by a species; but this fact can be of little 
classificatory value owing to the very large number of species 
which possess the same structure and arrangement of the chroma- 
tophores. 
2. The outward form of the cell, as seen in front view, varies 
within certain limits, which are usually very small, but which may 
in exceptional cases be considerable. The form of the vertical 
view is, as a rule, a more constant feature than the form of the 
‚Front view. 
3. The ornamentation (scrobiculations, granulations, spinula- 
tions, de.) of the cell-wall is relatively constant, being always 
arranged according to a definite law, which is only transgressed 
by variations in one or more of the individual component groups 
which constitute the pattern of arrangement. 
4. The prolific growth and rapid division of immense numbers 
of Desmids have atendency to produce variations from the typical 
forms. 
5. Changes in the conditions of environment cannot affect the 
characters of a species unless they act for long periods of time. 
II.— Variations in Form and Symmetry. 
Considerable diffieulties are encountered in the attempt to 
cultivate these plants under perfectly natural conditions, and all 
the variations described were found in a state of nature. The 
following is a selected account of a few of those that I have 
observed during a prolonged study of the Desmidiez. 
Under this heading are included variations in the arrangement 
and disposition of the markings adoruing the cell-wall; and I 
would here urge the plea that all published figures of Desmids be 
made strictly accurate in detail, and not drawn approximately so. 
In recent years many very inaccurate drawings have been 
published, not only of previously deseribed species, but also of 
new species and varieties *. Though it may seem presumptuous 
* That this is not the only branch of microscopical science in which gross 
inaccuracy with regard to detail is prevalent is clearly seen from remarks 
made by C. F. Rousselet, ** Second List of New Rotifers since 1889," Journ. 
Roy. Mier, Soc. 1897, p. 10, in which he states that some of the published 
“figures and descriptions are quite useless as aids to further identification.” 
He also remarks that “it would be very desirable in the interest of science if 
