satisfactory a condition. All kinds of media have been suggested,
but, after all, the water in wliioh the specimens are found
has been proved the most suitable, since it does not disturb the
endochrome, which any fluid of greater density would do. I f it
IS considered desirable to preserve the green colour the slides
should not be exposed to the light more than is absolutely
necessary. Another method of preserving specimens for future
J i d y ,s to dry them on small squares of paper or thin mica.
These can be moistened at any time, and the specimens
examined, but unfortunately in a deteriorated condition, for the
endoehrome will disappear and the cells collapse. The free use
oi the pencil and carnera-lucida in making drawings to an
uniform scale from the fresh specimens is, after all, the very best
course. j
No excuse need be offered for the production of the present
work since its want has been felt for many years. We can only
hope that It may answer all reasonable expectations
May, 1887.
M. C. 0.
BRITISH DESIIDS.
Order I. Z YG O PH YC EÆ .
Either cellular or multicellular algæ, with terminal vegetation,
and destitute of true ramification. Cells single, segregate,
or geminate, or united in a series. Chlorophyll-mass for the
most part distributed in plates, or bands, including one or more
amylaceous granules.
Multiplication by division of the cells in one direction.
Propagation by zygospores, resulting from the conjugation
of two cells. (See “ British Fresh Water Algæ,” p. 74.)
F amily I. DESMIDIERE.
Unicellular algie. Cells for the most part compressed, single,
segregate, or gemmate, or a larger number united in a band, or
filament; variable in form, usually constricted in the middle,
so as to constitute two symmetrical semi-cells.
Minute unicellular algas, inhabiting fresh water. Cells consisting of
two symmetrieal equal portions, their junction marked by a pale interruption
of the endochrome. and frequently by a oonstriction._ devoid of
silex: increasing by the formation of two new half-cells, mteposed
between the two halves of the older cell. Cells either becoming free or
united into a filament. Endochrome green. Eeproduotion by o onjup-
tion of the contents of two distinct cells, which result in the production
of zygospores, the contents of which afterwards become differentiated into
young cells of a new generation. Ciliated zoospores (m one species only)
produced by conversion of the endoohrome.
Sect. A. L biosporjí!.
Sect. B. CosMospoEJt.