Criistaceans. 



37 



that these Decapods fall into two main divisions, according 

 to the condition of the abdomen — one in whicli it is conspicuous 

 and stretched out , as in the lobster ; the other in which it is 

 reduced and held permanently flexed in a groove on the lower 

 surface of the carapace, as in the crabs. The forms with con- 

 spicuous abdomen have been named long-tailed, Macrura ; the 



FIG. 37. LOBSTER. 



carapace is generally shoi-fer than the abdomen and is produced 

 in front into a pointed " prow " or rostrum, the eyes are not 

 sunk in orbits, and the abdomen terminates in a fan-shaped 

 flap formed by the tail-piece and the enlarged last pair of 

 appendages. For practical purposes the Macrura may be divided 

 into creeping and swimming forms. The former include our 

 two most important edible crustaceans, the lobster and the 

 crawfish or spiny lobster [langousie of the French hotels). The 

 Lobster {Homarus vulgaris), ioo well known to require description 

 here, lives among rocks well below low-water mark, and is not 

 often seen close to the shore (Fig. 37). It breeds between July 

 and September, and the eggs, three thousand to ten thousand in 

 number, are carried by the female, attached to the abdomen ; 

 they take ten to twelve months to hatch, and the free-swimming 

 larvffi which issue from them require four months before attain- 

 ing the perfect form and assuming the crawling habits of their 

 parents. The growth is a slow one ; six to t^n 5'ears are required 

 for a lobster to reach a length of ten inches, and it has then 

 passed through something like twenty moults since it left the 

 larval condition. In moulting, the flesh}' parts of the limbs 

 are withdrawn first, and the whole animal then passes out ' 

 through a slit between the thorax and abdomen. The operation '\ 

 does not take more than half an hour, but it requires tliree or ) 

 four weeks before the new carapace acquires its full thickness/ 

 and hardness. While in tlie soft condition, after leaving its 



