226 Report of the Microscopical Section. [Sess. 
anterior pair of which are of a very peculiar construction. 
This pair is so modified that each foot-jaw forms a short 
hollow cylinder fitted at the extremity with a horizontal rim, 
furnished round the margin with strong sete. Attached to 
the inside of these cylinders are seen four strong muscles, by — 
which they are actuated. These cylinders, with their rims — 
and strong sete, act like suckers, and enable the animal to 
fasten itself securely to its host. 
There are four pairs of swimming feet by which the Argulus 
can move about in the water when it is not attached to a fish. 
These feet serve also for the purpose of respiration, and are 
fringed with beautiful plumose sete. 
Unlike the Apus, the Argulus has no external ovisac, but in 
a gravid female the eggs may be seen in the cavity of the 
thorax, between the two lateral prolongations of the carapace. 
The abdomen is by some described under the name of the tail. 
It consists of a bilobed plate, in the bifurcation of which is 
situate the anus. 
The other Entomostraca studied were of much smaller size. 
We shall take them in their order. 
Daphnia.—The Daphnia is one of the genera belonging 
to the family Daphniadz, and of the order Cladocera, so | 
called from their antenne resembling somewhat the branched 
horns of a stag. The species studied was the Daphnia pulex, 4 
or water-flea. This name appears to have been given to it on | 
account of its form somewhat resembling the parasite in ques- 
tion, and also from its jumping motions through the water. 
Daphnia pulex is sometimes common in ponds and ditches 
of standing water. During its life the creature moults very — 
frequently, this moulting taking place every ten days or a 
fortnight, according to the warmth of the weather. Viewed 
externally, the Daphnia appears to consist of two very distinct 
parts—the head, which carries the eyes, antenne, and the ~ 
apparatus of the mouth; and the thorax and abdomen, which — 
bear the branchial legs, and are covered by a very transparent _ 
shell. The head is also covered with a shell of somewhat 
harder consistency than that which covers the thorax and — 
abdomen. The prolongation forward of this covering of the 
head forms a point somewhat resembling the beak of a bird. — 
Beneath this beak are the superior antenne, consisting of a — 
