CRUSTACEANS 
the crayfish. The species of woodlice in England amount to more than 
a score. Many of them are so generally distributed that it will be no 
exaggerated estimate to credit Bedfordshire with half a score of them. 
Mr. James Saunders assures me that he often meets with them when he 
is hunting for mycetozoa, and certainly in that or any similar research 
Philoscia muscorum (Scopoli) could not well fail to be met with. Oniscus 
asellus, Linn., Porcellio scaber, Latreille, and Armadillidium vulgare 
(Latreille) make themselves familiar everywhere. But none, even of 
these the commonest of the common, appear to have been specially 
recorded for this county. 
The two sessile-eyed groups agree in the character of the eyes. 
They agree in having seven segments of the middle body freely movable, 
and not as in the Decapoda covered by the carapace. They agree also 
to a great extent in the distribution of their appendages, for they follow 
up the two pairs of antenne, not by six pairs of jaws and five pairs of 
trunk-legs, but by four pairs of jaws and seven pairs of trunk-legs. But 
these features of agreement do not exclude strongly-marked differences. 
The Isopoda, whether terrestrial or aquatic, being usually flattened from 
above downward, are fitted for walking; whereas the Amphipoda, being 
as a rule laterally compressed, in clumsy attempts at an upright gait 
commonly fall over on one side and have to slidder. A more important 
distinction depends on the position of the breathing organs. ‘These in 
the Amphipoda are sacs or vesicles, simple or pleated or twisted, attached 
to some or all of the trunk-legs except the first pair. In the Isopoda 
they are not in the trunk or middle body at all, but in the tail part, 
otherwise known as abdomen or pleon. Some of the appendages of this 
pleon, the thin-skinned flattened pleopods, are respiratory. The equi- 
valent appendages in the pleon of the Amphipoda have no such function, 
although they may be considered in some measure auxiliaries to it. 
That the Amphipoda are represented in Bedfordshire does not rest upon 
conjecture, for early in February, 1902, Mr. James Saunders very oblig- 
ingly collected from the river Lea near Luton some specimens which he 
packed in damp moss and dispatched by post. They reached me the 
following day, languid but still alive, and proved to be, as Mr. Saunders 
supposed, the wide-ranging Gammarus pulex (Linn.). This may be taken 
as a typical representative of the Amphipoda at large, but especially of 
the Gammaridea, the most extensive of the three sections into which the 
whole group has been divided. Just as nature has been at the pains to 
distribute Ase//us aguaticus (Linn.) over all parts of England as if with 
intent to provide a type of water-breathing isopods, so has Gammarus 
pulex in the companion group been made everywhere available. At all 
events no English naturalist can excuse an utter ignorance of sessile-eyed 
crustacea on plea or pretence that specimens are not procurable for 
investigation. The beginner will soon find his wits well exercised if he 
attempts to compare the common freshwater gammarus with two other 
species that are common on the seashore, namely G. Jocusta and G. marinus. 
He might at first impatiently refuse to believe that the three species 
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