ON ACANTHOLEBERIS. 57 
of mud, Diatoms, and Desmids which render it so difficult a 
matter to see the structure of the organs of the body contained 
within the carapace. That the coating of extraneous matter is 
the effect, and not the cause, of the mability of the animal to 
swim is proved by the fact that one of the specimens obtained, 
which was sent to Mr. G. 8. Brady for the purpose of obtaining 
his kindly extended and valuable aid in the delineation of the 
species, gave birth to five young while in his possession; and he 
informed us that though these young when first born, were able 
to raise themselves slightly in the water, yet it was not more 
than about half an inch, nor could this be effected without great 
effort, or, apparently, without the assistance of the sides of the 
vessel in which they were contained; and when two or three 
days old, even this limited power of locomotion was lost. Mr. 
Brady wrote to us the following vivid description of the motions 
of these young specimens:—“ It is a sight to see the brutes 
swim, or try to swim, under the microscope. When a good view 
from the dorsal aspect is obtained, one sees that they put their 
two great antenne together, and strike out in a good bold sweep 
like any Christian, the superior antenne working synchronously, 
but in a smaller arc, inside the greater ones. The motion of 
these lesser antenne is very beautiful; and the muscular con- 
tractions in the basal joints of the greater ones.are remarkably 
plain, throwing the limb into great wrinkles. When the animal 
is tired of this sort of exertion, it stops its arms, and begins 
working its branchial apparatus at a great rate; but, so far as I 
can see, the two systems are never in active motion together. 
They seem to attract dust and parasitic growth; for, though 
kept in simple water, they are surrounded with confervoid fila- 
ments, Diatoms, Oscillatorie, &c.” 
Another remarkable feature in the history of this Daphnian 
is the great scarcity of the species individually. Asa rule, where 
an Entomostracan occurs at all, it is to be met with in abund- 
ance. ‘This is very far from being the case with A. sordida. 
Failing in the attempt to make out the structure of the three 
specimens we had obtained in the Bishop-Middleham colliery 
pond, and being unwilling to destroy them by attempted dissec- 
