XII] 



DECAPODA 



219 



chambers on each side of the body. The gills of course are outside 

 the body, but are in special chambers bounded by the branchio- 

 stegites or free edges of the carapace. 



The An om ura are in some respects intermediate between the 

 foregoing and the following division. As in the Crabs the 



la 



-8 



FIG. 86. 



B 



A. Left side of a larva of the Prawn, Penaeus, to show the origin of the 

 gills. Slightly magnified. From Glaus. Lj to L 6 . The first to fifth 

 ambulatory limbs. Mj to M 3 . The first to third maxillipedes. la, 2a, 3a, 

 7a. Podobranchs. Ib, 5b. Anterior arthrobranchs. Ic, 2c, 7c. Pos- 

 terior arthrobranchs. Id, 5d, 7d. Pleurobranchs. Of these rudiments 

 of gills only nineteen develop. B. Left side of a fully-grown Prawn, 

 Penaeus semiculcatus, to show fully-grown gills. Slightly magnified. 

 8. Exopodite of second maxilla, which flaps to and fro and so causes a 

 current over the gills. 9. Exopodite of fourth ambulatory limb. 



abdomen is folded somewhat forwards but the tail-fin although 

 reduced is retained. The last pair or last two pairs of the thoracic 

 limbs are reduced and turned dorsalwards. Some species the 

 Hermit-crabs shelter themselves in the empty shells of molluscs. 

 In these cases the abdomen does not develop a hard covering, as 

 the animal is sufficiently protected by its lodging. It remains soft 



