( o 



rigid and often hook-like, and having a large patch of imbricating corneous 

 granules — possibly acting together as a sucker — on the dorsal surface. 



Sometimes the uropods are the only abdominal appendages present, but 

 always in the female, and usually in the male also, there are 3 or 4 (somites 

 2-4. or 2-5) unpaired appendages on the left side ; only in the unique 

 Paguropsis is their position indifferently either left or right. These unpaired 

 appendages are large in the female, where they are used for carrying the 

 eggs; but are small and uniramous, or have one ramus rudimentary, in the 

 male, where they are of no functional importance. Sometimes, in addition 

 to the unpaired appendages, the ist, or ist and 2nd, abdominal somites of the 

 male, and the ist of the female are furnished with umr^imoxxs, paired appen- 

 dages modified for sexual purposes. Very rarely (only in the Pylochelida) 

 do paired appendages exist on all the abdominal somites from the ist to 

 the 6th. 



As regards the uropods and telson, they may be quite symmetrical, but 

 are usually much more developed on the left side than on the right. 



3. Organs of Respiration. 



The gills are variable both in form and number, but are never more than 

 14, or less than 10, on either side. Five pairs of arthrobranchise are always 

 present, namely, a pair on each of the thoracic appendages from the external 

 maxillipeds to the 4th pair of legs (somites IX — XIII): in addition, each 

 of the last four thoracic somites may carry a pleurobranch ; or the pleuro- 

 branch may be absent from the last somite only ; or may be present on the 

 penultimate somite only ; or all the pleurobranchise may be absent. 



The gill-plumes may be phyllobranchise (two series of leaves, one on 

 either side of a shaft), or trichobranchia; (four series of filaments, two on 

 either side of a shaft), or may be intermediate in character. Most often they 

 are phyllobranchia;. 



In the land-hermits the gills are of quite subsidiary importance, and 

 respiration is in a large measure effected either by the wall of the gill 

 chamber or by hypertrophied portions of the integument of the abdomen. 



4. Reproduction. 



The reproductive organs are lodged in the abdomen and are to a certain 

 extent affected by its lop-sided character. Their ducts perforate, in the 

 male the coxae of the 5th pair of thoracic legs, in the female the coxae of 

 the antepenultimate pair. 



The ova are impregnated internally, probably- — when such mechanisms- 

 are present — by the paired anterior abdominal appendages of the male, or 



