536 ORGANS OF RESPIRATION. 



where they are concealed beneath the sides of the dorsal 

 carapace, in a thoracic cavity separated by a tendinous 

 diaphragm from the abdomen. 



In many of the lower suctorial parasitic Crustacea, as the 

 califfus, no special organs for respiration have been detected, 

 and they may be aerated through the soft naked surface of 

 their body. The branchiae have the simple form of flat vas- 

 cular membranous folds, or vesicular lamellae, attached to 

 the thoracic feet in most of the branchiopodous species. 

 They are also, in the amphipoda, in form of membranous 

 foliated expansions, highly vascular, attached naked to the 

 thoracic feet, and rapidly moved to and fro by them, for the 

 aeration of the venous blood extensively spread on their sur- 

 face ; they form small membranous sacs attached to the tho- 

 racic appendices in the laemodipoda. They are exposed 

 membranous, sometimes ramified laminae, attached to the 

 abdominal feet, in the isopods ; and, with the same position, 

 in most of the stomapods, as in the squillae, they consti- 

 tute flabelliform series of small pectinated tubes, while in 

 others of the same order, as the cynthiae, they form a small 

 pedunculated membranous cylinder. The five pairs of broad 

 natatory abdominal feet of the limulus support, on their 

 posterior surface, innumerable delicate exposed branchial fila- 

 ments, composing the respiratory organ; and the anterior 

 five pairs of abdominal feet, in the squilla, support as many 

 pairs of peniform ramified tubular branchiae. 



The branchiae, or the elementary pieces of the feet sub- 

 servient to respiration, are, in the decapods, more developed 

 and more complex, though not more numerous, than in most 

 of the inferior Crustacea ; and they are disposed in two lateral 

 longitudinal rows of vertical laminated pyramids, attached to 

 the bases of the five pairs of ambulatory, and the three outer 

 pairs of masticatory, appendices. They are concealed in a 

 respiratory cavity, formed by the lateral overhanging folds of 

 the carapace, which gradually extends downwards, to cover 

 them during their earlier development ; and in this cavity 

 they are fixed below by the bases of the several branchial 

 foliated pyramids, and their free apices converge above. In 

 the brachyourous decapods, the branchial laminae composing 

 the ten or eleven vertical pyramids on each side, are more 

 simple, and present a smaller extent of surface for the distri- 



