1g00-1901.] Report of the Microscopical Section, 223 
Entomostraca: “Animal aquatic, covered with a shell or 
carapace of a horny consistency, formed of one or more pieces, 
in some genera resembling a cuirass or buckler, and in others 
a bivalve shell, which completely or in great part envelops 
the body and limbs of the animal.” 
The text-book followed was Baird’s ‘Natural History of 
the British Entomostraca,’ and one species was studied under 
microscopical dissection from each of the following genera, and 
in the order stated—viz., Apus, Argulus, Daphnia, Cypris, 
Cyclops, Canthocamptus, and Diaptomus. 
Apus.—The genus Apus belongs to the Apodide, a family of 
the large legion of the Branchiopoda, or branchial-footed animals. 
The species which engaged attention was the Apus cancriformis, 
Schaeffer, a comparatively large crustacean inhabiting stagnant 
waters. The length of this species, inclusive of the tail 
appendages, is about an inch and a half. The head and 
thorax are covered by a carapace in the form of a shield, 
with a deep indentation at the posterior end. It is of a tough 
flexible nature, and is composed of three layers. The outer 
layer is chitinous, of a light-brown colour, and very trans- 
parent; the median layer is spongy, of a bluish-grey colour ; 
while the innermost is composed of an extremely thin, trans- 
parent membrane. The carapace externally is convex, rising 
to a central longitudinal ridge. In the median layer on each 
side of this longitudinal ridge are three or four well-marked 
lines running obliquely in an arched form, thus following the 
contour of the’ outer edge of the carapace. ach of these lines 
is reflexed or bent back upon itself, thus forming a series of 
loops, the one inside the other, like a nest of test-tubes. The 
older writers regarded these as blood-vessels; they are now 
called the shell glands. They are very clearly seen by the 
naked eye if the carapace be removed and laid upon its back. 
From the anterior part of this median layer spring the muscles 
which actuate the mandibles. These mandibles are very power- 
ful, being upwards of one-tenth of an inch in length, and each 
armed with eight strong teeth. 
The outer layer of the carapace covers the whole of the 
tergal aspect of the head, and, extending over the snout, turns 
backward on the ventral aspect, and forms the covering of a 
membrane which extends to the mouth, and from which the 
