E. A. Andrexos — Anatomy of the Spider Crab. 115 



carapace, througli the thorax and enters the abdomen. It gives off 

 two branches in tlie tliorax and several small ones in the abdomen, 

 along the dorsal part of which it passes a little to the left of the 

 median line. The inferior abdominal artery (/'", fig. 20) is of abont 

 the same size as the superior. It runs back along the sternal part of 

 the abdomen, turning to one side of the median line, and gives 

 branches to the ilexor muscles. Near its origin a long slender 

 branch passes up to the intestine on the surface of which it ramifies. 



The blood from the arteries collects in sinuses and then in cavities 

 under the branchije, whence it passes into the afferent vessels of 

 those organs («/", fig. l). 



In each branchial chamber the branchiro are nine in number; they 

 form a conical mass, resting on the lateral walls of the body at an 

 angle of about forty-five degrees. The four larger ones are attached 

 in a longitudinal row, the posterior two [hr 6, hr 1, fig. 1), each to an 

 opening in the pleural wall above the insertion of second and third 

 ambulatory limbs respectively, the anterior two {br 4, br 5), to the 

 articular membrane of the first or chelate leg. Three smaller 

 branchite {br 1, br 2, br 3), the shortest of which does not extend 

 quite to the apex of the branchial chamber, ai-e attached in a trans- 

 verse direction, owing to the constriction of the body in front of the 

 ambulatory legs. The outer two (br'', br^) are attaclied to the 

 articular membrane of the third maxilliped ; the innermost and 

 smallest {br 1), to that of the second maxilliped. Closely applied 

 to the bases of these branchiae and filling out the general conical 

 outline, are the two remaining branchije, which are mucii smaller and 

 are attached to the epipodites of the first and second maxillipeds 

 {br, figs. 12, 13). 



Each branchia consists of an anterior and a posterior series of 

 closely set horizontal laminae, connected by two vertical vessels, an 

 outer, afferent {af, fig. 1), and an inner, efferent {ef, fig. 1), which 

 communicate with cavities in each lamina. The whole has the shape 

 of a quadrangular pyramid attached at its base. The integument of 

 the branchise is a thin chitinous cuticle continuous with the integu- 

 ment of the body. To aerate the blood in the laminaj water is con- 

 stantly drawn into the chamber through the afferent opening just in 

 advance of the basal joint of the chelate leg, being forced out 

 through the efferent canal by the working of the scaphognathite 

 {sg, fig. 10) ; and it is kept in motion by the epipodites {ep, figs. 11, 

 12, 13), within the chamber. 



The efl'erent vessels of the branchiae open into the branchio-cardiac 



Trans. Conn. Acad., Vol. VI, 1883. 16 July, 1883. 



