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, we 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 in 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 de- 



