brackish, and sea water: free or attached, single, or embedded in
gelatinous tubes, the individual cells (frustules) with yellowish or
brown contents, and provided with a silicious coat composed of two
usually symmetrical valves variously marked, with a connecting band or
hoop at the suture. Multiplied by division and by the formation of new
larger individuals out of the contents of individual conjugated cells;
perhaps also by spores and zoospores.

14. _Volvocineae_.--Microscopic cellular fresh water plants, composed of
groups of bodies resembling zoospores connected into a definite form
by their enveloping membranes. The families are formed either of
assemblages of coated zoospores united in a definite form by the
cohesion of their membranes, or assemblages of naked zoospores inclosed
in a common investing membrane. The individual zoospore-like bodies,
with two cilia throughout life, perforating the membranous coats, and by
their conjoined action causing a free co-operative movement of the whole
group. Reproduction by division, or by single cells being converted into
new families; and by resting spores formed from some of the cells after
impregnation by spermatozoids formed from the contents of other cells of
the same family.

[Illustration: MALARIA PLANTS COLLECTED AT 165TH STREET, EAST OF 10TH
AVENUE, OCT., 1881.

Plate IX.--Large group of malaria plants, Gemiasma verdans, collected at
165th Street, east of 10th Avenue, New York, in October, 1881, by Dr.
Ephraim Cutter, and projected by him with a solar microscope. Dr.
Cuzner--the artist--outlined the group on the screen and made the
finished drawing from the sketch. He well preserved the grouping and
relative sizes. The pond hole whence they came was drained in the spring