138 THE ZOOLOGIST. 
the chitinous membrane of the stomach. After this operation, as 
might be expected from their unprotected condition and defence- 
less state, the animals are of a retiring disposition, until the 
expanded body has formed a new secretion of lime; in other 
words, a new exoskeleton. This exuviation takes place frequently 
during the early life of the animal, but not so often in adults. 
There is, we think, some difficulty even yet as regards our 
knowledge of this period of exuviation, for we have just preserved 
a specimen of Lithodes maia, which, if size be any proof of age, 
was only half-grown. This specimen was just on the point of 
casting its shell, which was, however, covered with fine living 
Balani, or barnacles, more than two inches in height. 
We may here mention, as regards the mature female of many 
species, that it is just after exuviation, and when the new shell is 
still soft, that pairing usually takes place. 
Another remarkable feature of the life-history of the Crustacea 
is their power of reproducing lost limbs; under these circum- 
stances the ease with which they part with limbs under the 
influence of terror will be understood. This dislocation takes 
place at the narrowest joint of the imprisoned or injured limb, 
and the bleeding which ensues coagulates over the wound. The 
new limb is first produced in the form of a small tubercle, which 
enlarges at each successive casting of the exoskeleton, but which 
probably rarely attains to the size of its corresponding member. 
Species of the genera Xantho and Galathea are especially subject 
to this voluntary dismemberment. 
Reverting now to the subject of structure: the exoskeleton is 
divided roughly into three parts or regions—namely, the CEPHALON 
or head, the THoRAX, and the aspomeN. In the Brachyura, or 
Crabs, the head and thorax are united in one roughly oval or 
circular case, whilst the abdomen is but slight and bent under the 
thorax, fitting into an aperture between the leg-joints. In the 
Anomoura, among which may be instanced the Hermit Crabs, 
many of the forms have the thorax and head more elongated, and 
the abdomen soft and devoid of segments, protected by insertion 
in the dead valves of Mollusca. The Macroura (or Lobster 
forms) have the thorax and head generally cylindrical, and the 
abdomen developed into arched segments. ‘These segments are 
decisively separated, but the division of the head and thorax is 
only marked externally by a cervical groove, although the interior 
