No. 390.] THE DISTRIBUTION OF MALLOMONAS. 487 
nucleus, if present, is indistinct. At times a globular, balloon- 
like body is attached to the posterior extremity. It is appar- 
ently a development of the contractile vacuole. It is usually 
small and colorless, with a granular structure, but sometimes 
it is large, green, and spore-like. This body may be connected 
with some process of reproduction. Reproduction of Mallomo- 
nas takes place by sporular encystment. The protoplasm con- 
tracts, assumes a spherical shape, shrinks, and becomes invested 
with a thin integument. A single spore is formed by each 
individual. The liberated spores have a brown color and are 
occasionally surrounded by a gelatinous tegument. 
All the forms of Mallomonas observed by the writers, not- 
withstanding their variations in size and shape, may be properly 
included under the single species M. ploss/iz Perty. 
Fresenius (/nfustonsthiere, Abth. III, 1878) described a 
minute form, to which the name M. freseniz has been given. 
Zacharias (Forschungsberichte, Theil I, s. 16) has described a 
species which he calls M. acarotdes Zach. It differs from the 
type form only in having the setae thicker and more curved than 
those of M. plosslii (Vergl. sur Kenntniss kleinsten Lebensformen, 
1852, s. 83). He has also described (Forschungsberichte, Theil 
I, s. 73) a new variety which he has called M. acaroides Zach. 
var. producta (Seligo). It differs from the previous form by its 
larger size and by its longer spines. Seligo (Ueber einige Flagel- 
laten des Stisswasserplankton, Jan. 3, 1893), under the name 
Lepidoton, has described the same form. 
Mallomonas is of interest to students of aquatic life because 
of its peculiar vertical distribution during the summer. Three 
instances of this are on record; namely, in Lake Cochituate and 
Whitehall Pond, of the Boston supply, and in Ridgewood Reser- 
voir, of Brooklyn, N. Y. 
Lake Cochituate is a lake of almost colorless water, with a 
maximum depth of sixty feet and with well-marked stagnation 
periods. Mallomonas is often found there in numbers varying 
from 50 to 100 per cc. On June 24, 1896, it suddenly ap- 
peared in the lower strata of water near the gate house. There 
were 116 per cc. at the mid-depth -thirty feet, 42 per cc. at the 
bottom sixty feet, but none at all at the surface. The follow- 
