CRUSTACEANS 
again that myriapods, without being either insects or crustaceans, are 
possessed of antenne. But the point that chiefly concerns our present 
subject is the fact that crustaceans are distinguished alike from myriapods 
and insects by having the pairs of antenne twofold. It cannot be said 
however that they always make quite as much of this distinction as they 
might. In the woodlice the first pair of antenne are exceedingly small 
and often hidden away as if these isopods were ashamed of them. Also in 
Talitrus, the sandhopper, a genus of semi-terrestrial amphipods, a similar 
diminution occurs. In many of the Entomostraca likewise the first 
antenne are small and inconspicuous, and that is the case with more than 
one of the species presently to be mentioned. 
The Entomostraca are at present divided into three principal sec- 
tions—Branchiopoda (branchial-footed), Ostracoda (shelly), Copepoda 
(oar-footed). Not much of the nature in each case can be explained by the 
mere meaning of the name. The Ostracoda are called shelly because, 
like some mollusca or shellfish, they have the body capable of a complete 
enclosure between two valves. But some of the Branchiopoda have a 
similar bivalvular security, entitling them to boast equally with the 
Ostracoda that the carapace is their castle. ‘The Copepoda use their 
feet for locomotion in the water, but so far as that is concerned there are 
some of the stately phyllopods to which the name of oar-footed would 
as well or even better apply. 
The Branchiopoda are divided into Phyllopoda (the leaf-footed), 
Cladocera (the antlered), Branchiura (the branchial-tailed). The last is 
by far the smallest of the three divisions, and has in England only a 
solitary representative, Argulus foliaceus (Linn.). It so happens however 
that this is among the very few recorded crustaceans of Bedfordshire, 
yet it comes into the list by what sportsmen would probably call a fluke, 
for the mention of it is not in any discussion of its own class, but only 
as incidental to ichthyology. In a paper on ‘The Fish of the River 
Ouse, Mr. A. R. Thompson observes that ‘the Argulus foliace (or 
roach louse) is also found upon roach and other coarse fish: it is a small 
crustacean of a disc-shape and attaches itself by means of two suckers on 
the underside.’ It is a vicious little parasite, varying in length when 
adult from an eighth to nearly a third of an inch. Fishes that would 
seek revenge by swallowing their foe are soon glad to give it up again. 
Scientifically it is interesting as belonging to a very small yet distinct and 
widely-dispersed group. It was at one time placed not in the Branchio- 
poda but among the parasitic Copepoda. Its mouth organs are con- 
siderably modified from any normal standard, the first pair of maxille 
being evanescent or lost, while the second pair are metamorphosed into 
suckers. These, as above mentioned, are the organs of adhesion. For 
sucking the juices of its victim its uses, not the suckers, but its mouth, 
an efficient apparatus being formed by the sharp glandular organ called 
the stimulus, and by a combination of the lips and mandibles. 
1 Abs. Proc. Trans. Beds Nat. Hist. Soc. and Field Club for the years 1882-3, 1883-4 (May, 
1885), Pp. 93. 
95 
