4 
BRITISH ENTOMOSTRACA. 
part ignorant of them, which they nevertheless produce 
in the economy of nature ;* that these things are very 
worthy of being known scarce any one will doubt. Not 
to mention their external similitude to shells, and the 
natural transition which takes place in them, from insects 
to testaceous animals, who ever knew, before the Cypris 
was detected, of an insect quadruped? Before the 
Limulus and Caligus were properly observed, who ever 
knew of an insect acephalous, or with a head at least 
scarcely visible ? Who ever imagined of a copulation of 
two males with one female at one time, such as takes 
place in the famous Fulex aquaticus ? or of an animal 
whose head was all eye, as we see in the Polyphemus ? 
These and more wonders are to be met with in the history 
of the Entomostraca.” 
The greater number of these little creatures are 
furnished with branchiae, either to their feet or maxillae, 
and when noticed in their native habitats may be seen 
to have them constantly in motion, their action being 
seldom interrupted. One chief use, therefore, of them 
in the economy of nature, may be, as Muller says, to 
ventilate the water day and night ; and as they chiefly 
reside in standing pools, they may thus be of great use 
in preventing them from becoming soon putrid. As 
this may be considered one of the benefits conferred 
by these insects, it may be useful to know the evils 
to man they may be likely to produce. Though they 
are most abundant in stagnant water, they yet occur 
in considerable numbers in the purer sorts of water that 
serve as our common drink, and may frequently be seen 
even in the drinking-water of London, Edinburgh, and 
other large towns ; and Muller asserts very gravely, that 
as we thus drink them alive, and with their eggs, he 
would not be surprised were we to discover them some 
day in the human intestines. “ The time,” he says, “ is 
at hand, when the causes of disease shall not only be 
* “ It is the common opinion that it is the Caligi which force the salmon 
from the sea, up rivers towards the waterfalls.” 
