540 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



first antenna another type of setae is found. They are 

 in a dense bunch on the upper side of the exopodite and 

 are known as olfactory setae. Each seta is a long, 

 tapering, flattened shaft, with a large number of joints — 

 about two dozen- — placed on a wide base. It is hollow 

 and appears to open by a minute pore at its distal end. 

 Round each basal joint is a small bunch of minute hairs. 

 The exopodite is a strongly annulated conical structure, 

 and each ring bears several of these long setae. In life 

 the crab continually flicks its antennules, spreading the 

 setae at each flick. Each seta is supplied with a large 

 number of nerve fibres. 



MUSCULAR SYSTEM. 



It is unnecessary, for the purposes of this Memoir, 

 to enter into a full description of the muscular system of 

 the Hermit Crab. A detailed account of the muscles of 

 a fairly typical Decapod Crustacean has been given in 

 the Memoir on Cancer * ; and though the present type 

 has closer affinities with the Macrura than with the 

 Brachyura, so far as the present system is concerned, no 

 useful purpose will be served by enumerating muscles 

 which have their counterpart throughout the Order. 

 Certain parts, however, of the muscular system have 

 undergone profound modification due to the mode of life 

 of the animal, and of these parts an account, based 

 entirely on M. T. Thompson's f work on the meta- 

 morphosis, will now be given. 



It is the musculature of the abdomen which diverges 

 in the greatest degree from the normal. As practically 

 all the movements of the abdomen are confined to 

 flexion, the flexor muscles have become abnormally large 



* Pearson, " Cancer " L.M.B.C. Memoirs, XVI. 

 t Boston Soc. Nat Hist., Vol. XXXI., No. 4, p. 147. 



