36 A HISTOEY OF EECENT CEUSTACEA 



reverse. These organs are sometimes most dwindled in 

 families which can claim a decided precedence over others 

 in which these appendages are well developed. Thus they 

 are short in the crabs, but long in the lobsters and shrimps, 

 and short in the normal Isopods, but long or large as a rule 

 in the Amphipoda, and within the Amphipoda they are 

 short in the Orchestidte, a family that claims superiority 

 by its tendency to terrestrial habits. 



Those who have made themselves acquainted with 

 Professor Huxley's volume, ' The Crayfish,' in the Inter- 

 national Scientific Series, will be aware that in describing 

 a crustacean appendage he names the first two joints the 

 29rotoj)odite, which bears at its extremity on the inner side 

 the endopodite, and on the outer side the exopodite. For 

 these terms the shortened forms exopod and endopod will 

 here be preferred — exopod for exopodite, endopod for 

 endopodite and protopodite combined — and peduncle will 

 be used for a variable number of basal joints. In the first 

 antenna the peduncle consists, as already stated, of three 

 joints, and by this circumstance the rule which widely 

 prevails elsewhere that the so-called protopodite ends with 

 the second joint of an appendage is broken without any 

 obvious cause. Moreover, that which by its ''function and 

 in general by its superior size appears to be the main 

 branch is here the outer one, and not as usual the inner. 

 It is conceivable that the exopod is wanting, that the main 

 branch or principal flagellum is the true endopod, and that 

 the secondary flagellum is an independent outgrowth. 

 For the reasons mentioned, and some others, Dr. J. E. V. 

 Boas considers that the first antenna are not homologous 

 with the following limbs, but that both they and the 

 stalked eyes ought to be regarded as limb-///re sense 

 organs. That besides being organs of touch, they are 

 frequently organs of other senses, seems to be beyond 

 doubt. In the Macrura at large the first joint contains 

 an auditory apparatus. Sometimes the cavity is provided 

 with a well-formed otolith or ear-stone. In the lobster 

 and crayfish, Mr. Spence Bate says, ' the perforation is 

 long, narrow, and slit-like, the aperture being scarcely 



