80 LOBSTERS. 



sub-order Macrura (or long-tailed) ; family " Homarus 

 Vulgaris." The Crustaceans derive their name from the 

 fact that their bodies are wholly covered with a crust or 

 external skeleton (usually referred to as an exoskeleton] giving 

 rigidity and support to the internal organs ; and to its 

 inflections and projections the muscles and membranes of the 

 body and appendages are attached. They are thus the 

 opposite in all particulars to all the vertebrates (including 

 ourselves), whose bodies are built up on an internal skeleton. 

 Hence whilst we may be correct in saying of man " beauty is 

 only skin deep," of lobsters and such like animals their beauty 

 is only bone deep, and the moment their exoskeletons disappear 

 ugliness appears. 



The chemical composition of the shell of a lobster differs 

 somewhat according to whether it is just about to moult, has 

 recently moulted, or is well away from that periodical 

 characteristic, but, broadly speaking, the constituents as given 

 by Herrick may be taken to be 



Animal matter . . . . . . 45 '0 



Phosphate of lime . . . . . . 9'0 



Carbonate of lime . . . . . . 38'0 



Carbonate of magnesia . . . . TO 



Soda salts, &c. . . 7'0 



100 



and thus differs very considerably indeed from the com- 

 position of the shell of the common crab, in which the lime 

 is roundly double in quantity and the animal matter about 

 half. 



In common with all the higher Crustacea the skeletons of 

 lobsters consist of 21 typical segments, or somites as they 

 are called, each of which bears an appendage of some sort, 

 with the exception of the 21st, which we call the termination 

 of the tail but which has the scientific name of telson. 



