OB USTA CEA GILLS 



325 



tion the whole integument or a large portion of the same is capable 

 of respiration in a lesser degree. 



The respiratory functions in the Crustacea, as elsewhere, are 

 promoted and facilitated by various adaptations. Among these 

 we must note (1) the increase of the respiratory surface, the 

 outer integument, (2) the flowing of the blood to and from the 

 respiratory parts, (3) adaptations which serve to bring about a 

 continual change of the aerated water which bathes the respiratory 

 parts, and (4) adaptations designed for the protection of the neces- 

 sarily delicate-skinned respiratory organs. 



The principal increase of the respiratory surface is due to the 

 integumental fold which rises so generally from the head and appears 

 in very different forms as mantle, dorsal carapace, bivalve shell, or 



FIG. 226. Euphausia pellucida 9 (after G. O. Sars), cephalo-thorax (cth) and first abdominal 

 segment (a&j) from the side, h, Heart ; ovd, oviduct ; ov, ovary ; I, liver ; m, stomach ; era, eye ; a-[, 

 anterior, ao, posterior antenna ; ex^-ex^ exopodites of the 6 anterior thoracic limbs ; en\, en%, 

 endopodites of the 2 anterior thoracic limbs ; the 4 following are not drawn ; endo- and exo-podites of 

 the 7th and 8th thoracic limbs rudimentary ; &r r &r 8 , gills on the protopodites (I-VIII) of the 

 thoracic limbs ; 6r 1? first gill, a small epipodial appendage. 



cephalo-thoracic shield. Wherever this fold remains soft-skinned it 

 always helps in the respiration. It is often only the inner wall of the 

 fold which remains soft-skinned, and we frequently meet with adapta- 

 tions which serve for the purpose of setting in motion the water found 

 in the cavity between the fold and the body (respiratory cavity). 

 There are in Malacostraca (Zocea larvce, Tanaidce, Mysidce, Stomatopoda) 

 epipodial appendages of the maxillae or of the anterior thoracic feet, 

 which, during the movements of the limbs which carry them, vibrate 

 and cause a stream of water in the respiratory cavity in which they lie. 

 In a similar way in the Ostracoda the movement of the fan-like plates, 

 the so-called branchial appendages, which may occur on the 4th, 

 5th, and 6th pairs of limbs, bring about a constant stream of water 

 over the body surface. In the higher Malacostraca, especially in the 



