32 ZOOLOGY. 
tion is then carried on by the help of the lip alone, which 
expands latterly until it 
completely overlies the 
particle. All this is done 
quite rapidly, in a few sec- 
onds, and then the food 
glides quickly into the 
depths of the body, and is 
enveloped in a digestive 
vacuole, whilst the lip as- 
sumes its usual conical shape and proportions.’ (Clark.) 
All the monads have a contractile vesicle. In Monas 
termo, Clark observes that it is ‘‘ so large 
and conspicuous that its globular form 
may be readily seen, even through the 
greatest diameter of the body; and con- 
tracts so vigorously and abruptly, at the 
rate of six times a minute, that there 
seems to be a quite sensible shock over 
that side of the body in which it is em- 
bedded.”” The contractile vesicle is 
thought to represent the heart of the 
higher animals. The reproductive organ 
may possibly be represented in Monas 
termo by a ‘‘ very conspicuous, bright, 
highly refracting, colorless vil-like globule 
which is enclosed in a clear vesicle’’ called 
the nucleus. This and other monads live 
either free or attached by a slender stalk. 
As an example of the compound or aggre- 
gated monads may be cited Uvella, prob- 
ably glauconia of Ehrenberg. Other 
forms, as Codosiga, are fixed by a stalk to 
some object (Fig. 21, C. pulcherrimus 
Fig. 20.—Monads (Uvell/a).—After Tuttle. 
; : : Fig. 21.—A, Codosiga 
Clark). In this and allied forms the body puicherrimus’ “B. the 
: same beginning to under- 
is surmounted by a collar or calyx out of go fission, two new tl. 
. . Ha i 
which the flagellum projects. The Co- Feary spun indivi: 
dosiga has been observed by Clark to un- “After Clark. 
dergo fission, two independent monads resulting, within the 
space of forty minutes. 
