742 The American Naturalist. [August. 
" There exist organisms which lead a life of habitual isolation, but 
which understand how to unite for the purpose of attacking prey at 
the desired time, thus profiting by the superiority which numbers give. 
The Bodo caudatus is a voracious Flagellate possessed of extraordinary 
audacity ; it combines into troops to attack animacula one hundred 
times as large as itself, as the Colpods for instance, which are veritable 
giants when placed alongside of the Bodo. Like a horse attacked by 
a pack of wolves, the Colpod is soon rendered powerless ; twenty, 
thirty, forty Bodos throw themselves upon him, eviscerate and devour 
him completely. 
All these facts are of primary importance and interest, but it is 
plain that their interpretation presents difficulties. It may be asked 
whether the Bodos combine designedly in groups of ten or twenty, 
understanding that they are more powerful when united than when 
divided. But it is more probable that voluntary combinations for , 
• purposes of attack do not take place among these organisms ; that 
would be to grant them a high mental capacity. We may more 
readily admit that the meeting of a number of Bodos happens by 
chance. When one of them begins an attack upon a Colpod, the 
other animacula lurking in the vicinity dash into the combat to profit 
by a favorable opportunity. 
M. Binet compares the movements of the Protozoa in reproduction 
with those of the reproductive elements in the higher animals, — the 
spermatozoid and the ovum. He says : 
"A remarkable circumstance in this connection is, that the copula- 
tion of the spermatozooid and ovule is not without analogy to the 
copulation of the two animals from which they originated. The 
spermatozoid and the ovule, to some extent, repeat on a small 
scale what the two individuals perform in their larger sphere. Thus, 
it is the spermatozooid that, in its capacity of male element, goes in 
quest of the female. It possesses, in view of the journeys it has to 
make, organs of locomotion that are lacking in the female, and are 
useless to it. The spermatozooid of man and of a great number of 
mammifers is equipped with a long tail, the end of which describes a 
circular conical movement, which, together with its rotation about its 
axis, determines the forward motion of the spermatozooid. 
"The spermatic element, in directing itself toward the ovule to be 
fecundated, is animated by the same sexual instinct that directs the 
parent organism towards its female. 
"In the higher animals the movements of the spermatozooid that is 
endeavoring to reach the female exhibit a peculiar character which it 
