Sub-Glass 2. Malacostraca. Ordelr 6. Becapoda. 



225 



exopods. Of the abdominal limbs tbe last pair, bowever, is not yet present. It 

 is evident from this tbat the Cray-fish does not pass tbi-ougb a mysis-stage, nor, 

 so far as is known, through a prawn-stage. The young ones cling for a time 

 to the abdominal limbs of the parent. 



3. The Oraw-fish {Palinurus) are large, spiny Crustaceans, which 

 resemble Lobsters in most respects, although they difBer in that none of the 

 ambulatory limbs (aU of which are of about equal strength) are modified as chelae; 

 the second antenna is provided with a very long and strong fiageUum. A species 

 living on English coasts, P. vulgaris, can produce a creaking sound by 



Fig. 187. Phylloeoma, slightly enlarged. The four best developed pairs of i 

 are : third maxilliped, first to third ambulatory legs. 



rubbing the peduncle of the second antenna against a median projection of 

 the head. Scyllanis is nearly -related to the Craw-fish, btit differs from it in that 

 the long multiartioulate feeler is replaced by a short, broad, unsegmented plate. 

 The larva in both genera is very singular, hatching in the mysis-stage, 

 although the hinder thoracic feet are not yet present ; it is called Phyllosoma, 

 and is chiefiy characterised by its leaf -like and flattened form ; the carapace, 

 through which the branching of the liver may be seen, is a flat plate, and does 

 not cover over the whole thorax ; the latter is a roundish disc, at whose edge the 

 long locomotor limbs (the third maxillipeds and the ambulatory legs with small 

 swimming-rami) are articulated. The abdomen is an unimportant appendage. 



4. The Hermit-crabs (Pagurus) are characterised by having the abdomen 

 modified into a large membranous sac with hardly any muscles, but almost 

 entirely occtipied by the large liver, and the gonads, which have moved down 

 from the thorax. The abdomen is concealed in an empty gastropod shell which the 

 animal carries about ; it is always asymmetrical; its ventral side is 

 entirely membranous, but dorsally there are traces of the tergal portions of 

 the abdominal segments, as thin plates separated by large soft-skinned inter- 

 spaces: the last two segments alone are somewhat harder; the penultimate 

 iDears a small pair of abdominal appendages by which, with the help of the 

 seventh segment, the animal keeps in the shell. Of the other abdominal append- 

 ages only those of the left side are present (the first pair is often 

 •entirely wanting). The ambulatoiy legs are also peculiar ; the first pah- are 

 -strong chelae, the second and third simple walking legs, the fourth and fifth are 



Q 



