AKTHltOrODA. 



139 



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

 tail) is given to tViose ten-footed Crustaceans which Lave a long and 

 well-developed tail or abdomen. Amongst these are the Lobster, 

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

 be selected as a good tyi^ical example. 



In the Lobster or Cray-fish (fig. SV) the b(^dy is at once seen to be 

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



Fig. 67 —Tin: f.iiiiHinu Cray-lisl[ (Astaxus Jliiri^ 

 atilis), vieu'uii tViim brbjw. a Aiiteiinule.s ; h 

 Large anteiin.ii ; c Eyes ; d Opeiling of auditoiy 

 sac ; e Last X'air of foot-jaws ; / One the gveat 

 clielpe ; g Fifth thoracic limb ; ?i Swimiiierets ; 

 i The last pair of swiiiiinerets ; j The opening 

 of the anus Ijelow the telson. 



iM M 



'i.L,'. Ss. — Masticatory organs of 

 tli(.' Cray-fisli (Astacus jiuvia- 

 iilis). a Mandibles ; & Max- 

 illit; c Second pair of max- 

 illa^ ; c^ First pair of foot-jaws; 

 e Second pair of foot-jaws ; / 

 Third pair of foot-jaws. 



The so-called head is ccn-ered by a great .shield termed the " cara- 

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

 amalgamated segments which belong to the true head and to the 

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

 of a luunber (if segments wliicli are not immcvably nnited together, 



