AllTHKOPODA. 



139 



A. Macrura. — The name of Macrura (Gr. makros, long ; and oura, 

 tail) is given to those ten-footed Crustaceans which have a long and 

 well-developed tail or Jibdoraen, Amongst these are the Lobster, 

 Shrimp, Prawn, and Cray-fish, of which the Lobster or Cray -fish may 

 be selected as a good typical example. 



In the Lobster or Cray-fish (fig. 87) the body is at once seen to be 

 composed of two parts, familiarly called the *' head " and " tail." 



Fig. 87. — Tlie common Cray-fisli (Astacus fluvi- 

 atitis), viewed from "below. aAntennules; h 

 Large antennae ; c Eyes ; d Opening of auditory 

 sac ; e Last pair of foot-jaws ; / One the great 

 , chelie; g Fifth thoracic h"mb; h Swimmerets; 

 i The last pair of swimnierets ; j Tlie opening 

 of the anus helow the telson. 



Fig. 8S. — Masticatory organs of 

 the Cray-fish (Astacits Jluvia- 

 tilis). a Mandibles ; 6 Max- 

 illee ; c Second pair of max- 

 illie ; d First pair of foot-jaws ; 

 e Second pair of foot-jaws ; / 

 Third pair of foot-jaws. 



The so-called head is covered by a great shield termed the " cara- 

 pace," and it is in reality the cephalothorax, being composed of the 

 amalgamated segments which belong to the true head and to the 

 thorax. The so-called tail is really the abdomen, and it is composed 

 of a number of segments which are not immovably united together, 



