42 
OUR FRESHWATER ENTOMOSTRACA, SHELL- 
INSECTS, OR WATER-FLEAS. 
By W. BAIRD, M.D. F.L.S. 
O UR freshwater lakes, ponds, and ditches swarm with an in- 
finity of living creatures, and even our slow-running sluggish 
streams and rivers afford a safe habitation for numberless mi- 
nute species of the animal creation. Conspicuous amongst these 
denizens of the fresh water are the little Crustaceans known to 
zoologists by the name of Entomostraca. 
Distinguished, as a great majority of them are, by possessing, 
or appearing to possess, a single large eye, the species which 
were known to Linnaeus were almost all included by that cele- 
brated naturalist under the simple term Monoculus.* The 
most eminent, however, of all the succeeding earlier historians 
of these little creatures, the celebrated Danish zoologist, Otho 
Fridericus Muller, looking at them from another point of view, 
conferred upon them a different name. The singular appearance 
which most of them present, viz. annulose animals or insects 
covered with what appears at first sight to be a bivalve shell, 
supplied to him the appellation of Entomostraca,! or shell-insects , 
a name by which they are still known, and which has been 
retained by almost all succeeding authors. 
A great many of these shell-insects are natives also of the 
waters of our seas and estuaries, and play a by no means de- 
spicable part in the economy of creation. At present, however, 
we limit ourselves to the inhabitants of our fresh waters ; and, 
indeed, the interest attached to their history is great. Muller’s 
description of them is in elegant Latin, and his work J is still 
one of the most interesting memoirs in natural history. Jurine, 
in his work on the Freshwater Monoculi of the neighbourhood 
of Geneva, tells us that he had studied these little creatures for 
many years, and that each succeeding year only added to the 
interest he felt in them. 
* Monos (Greek), one ; oculus (Latin), eye. 
t Entomos (G.), an insect, ostrakon (G.), a shell. 
X Entomostraca, seu insecta testacea, quae in aquis Daniae et Norvegise 
reperit, descripsit et iconibus illustravit Otho Fridericus Muller. Lipsice et 
Hamits, 1785. 
