A HISTORY OF BEDFORDSHIRE 
were distinct one from another, but he would not easily persuade the 
latter two to live in fresh water, in which the first finds itself happy and 
at home. Without going into every detail, it may be pointed out that 
the sides of the head project angularly in G. /ocusta, but are rotund in 
G. pulex, and that the accessory branch of the upper antenne is more 
numerously jointed and longer in the former than in the latter. At the 
other extremity of the organism the last appendages, known as the third 
uropods, pretty well agree in these two species by having two elongate 
branches ; but in G. marinus the inner branch, instead of being only a 
little shorter than the outer, is scarcely a third of its length. In the 
Isapoda the appendages of the pleon form five pairs of pleopods (swim- 
ming feet) and one pair of uropods (tail feet). In the gammaridean 
Amphipoda there are three pairs of pleopods and three of uropods. In 
these pleopods each appendage consists of a stem with two many-jointed 
flexible setose branches, and this description, though admitting of some 
exceptions, applies with extraordinary uniformity throughout the group. 
When the animal is alive in its own element its natatory limbs are in 
tolerably constant motion, and that even when the body is stationary. 
The purpose of this is to keep a current of water continually bathing 
the branchial sacs, and when there are eggs in the mother’s pouch to 
give them also the benefit of the invigorating stream. ‘The maternal 
marsupium is formed by membranaceous laminz which, like the respira- 
tory vesicles, are attached to several of the trunk-legs at the upper part. 
In contrast to the pleopods the uropods have branches which are not 
flexible. ‘They seem to be purely locomotive, enabling the animal to 
make leaps or to jerk itself along, or in tube-building species to execute 
manceuvres which may best be described as turning head over heels. 
In almost every marine province the Malacostraca form a demon- 
strative portion of the fauna. It is only in specially favoured regions 
that they are conspicuous as occupants of fresh water. The other half 
of the crustacean class, upon which O. F. Miiller, towards the close of 
the eighteenth century, bestowed the designation Entomostraca, is rather 
differently situated. For, though these so-called ‘insects covered by a 
shell’ are extremely abundant in the sea, they also inhabit inland waters, 
not only with surprising diversity of form and ubiquity of range, but 
with no sort of regard for Malthusian prudence in their rate of prolifera- 
tion. In regard to this division of the subject there is fortunately some- 
thing to be gleaned from existing records. One quotation indeed might 
have been earlier given as applying not to a part of the class, but to the 
whole. The statement is of a character rather elementary, yet with 
certain reserves useful to be borne in mind. Ina paper on ‘ Antenna,’ 
Mr. H. J. Sheppard begins by saying : ‘Antenne are horn-like members 
placed on the head, peculiar to insects and crustaceans; the former 
generally have two, the latter more than two.’’ To this it might be 
objected that horns are usually stiff and antenne usually flexible; and 
1 Abs. Proc. Trans. Beds Nat. Hist. Soc. and Field Club for the years 1877-81 (Oct. 1, 1882), 
p- 20, 
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