326 



COMPARATIVE ANATOMY 



CHAP. 



Decapoda, the integumental fold, which becomes very hard and thick, 

 loses its respiratory significance, and as branchiostegite becomes a pro- 

 tective cover to the delicate gills which lie laterally in the respiratory 

 cavity under it. 



In the Balanidce a pair of fold-like projections of the mantle stand 

 out into the mantle cavity. These folds may again form numerous 

 lateral folds, so that the mantle surface is very much increased. 

 These formations have been assumed to be gills. 



In some Cyprididce (Osiracoda) the body carries on each side near 



the dorsal middle line, under the 

 shell, a row of small branchial 

 lamellee. 



The function of respiration 

 in the large majority of Crusta- 

 ceans is performed by the limbs 

 or their appendages. This is 

 comprehensible, since the change 

 of the water caused by the move- 

 ment of the limbs is of the greatest 

 use in promoting respiration. 



In many Lepadidce among the 

 Cmijjedia the tendril-like feet have 

 cylindrical or lancet-shaped ap- 

 pendages which with doubtful 

 accuracy have been indicated as 

 gills. They are found on the first 

 pair or pairs, and occasionally on 

 all of the tendril-like feet, and are 

 usually inserted on them near the 

 base. 



The leaf-shaped swimming feet 

 of the Phyllopoda are very well 

 suited for respiration. The ap- 



Fio. 227.— Transverse section througli the 

 oephalo-thorax of the Cray -fish near the heart, 

 diagrammatic. M, Branchiostegite ; k, gills ; kh, 



respiratory or branchial cavity ; ep, lateral waU ot pendages wMch are Called giUs and 

 the cephalo-thorax ; rtc, pericardium : h, heart ', sa, • , i , . ,-, . , 



sternal artery ; Z.hepatopancreas; d, intestine ; respiratory plates m thlS Order 



aim, ventral longitudinal muscles running to the have already been described. The 



abdomen; dbm, dorsal longitudinal muscles run- g^g ^f ^^J^g Phyllopodo, 8X& epipodial 



appendages, perhaps correspond- 

 ing with the gills of the Thora- 

 costraca. 



In the Leptostraca {Nebalia), 

 besides the delicate shell-fold, the lamellate thoracic feet function in 

 a special manner as respiratory organs. Their two branchial plates 

 (epipodite and exopodite) correspond with, the branchial and respiratory 

 plates of the PJiyllopoda. The branchial plate (epipodite) of the 

 proximal joint of the protopodite is morphologically equivalent to a 

 Decapodan gill. 



ning to the abdomen ; ivi, ventral chord ; sn, 

 subneural vessel ; bf, ambulatory foot ; vs, ventral 

 sinus ; ov, ovary. The arrows indicate the direc- 

 tion in which the blood flows (after Huxley and 

 Plateau). 



