CRABS AND SHRIMPS. 
209 
claws of the Crab ( Cancer pagurus) we see it at its maxi- 
mum of induration. 
The breathing organs furnish another point of diversity 
between the Crabs and Insects. In the latter they are 
air-pipes, in the former gills ; always contrived, though 
under many modifications of form and position, to extract 
the vivifying oxygen from water, and not from the atmo- 
sphere. Even the terrestrial species, as the common 
Woodlouse or Button ( Oniscus ), that rolls itself up into a 
ball in our gardens, need a certain degree of moisture to 
surround them, and hence they crawl out of their damp 
retreats only in wet weather. In the common Crab the 
gills are those long, finger-like, pointed pyramids of whitish 
substance often called “ dead men’s fingers,’ that are seen 
in two groups, when the carapace or “shell” is removed. 
If we examine them, wo shall find each pyramid to consist 
of a vast multitude of thin membranous plates closely 
packed together, but yet admitting the water to flow 
freely between them, which is kept iu constant circulation 
by means of innumerable cilia with which the surfaces 
are clothed. 
The increase of the race is effected only by means of 
eggs, no Crustacean that we remember bringing forth its 
young alive. Every one is familiar with the eggs, “ spawn,” 
as they are termed — of the Prawn, the mass of intensely 
red globules that is carried beneath the belly, and that is 
so difficult to remove. The difficulty arises from the 
manner in which the false feet, all fringed as they are 
with fine hairs, penetrate the mass ; and thus we perceive 
another use of these organs, besides that of locomotion, 
already alluded to. The eggs, as they are laid, are dc- 
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