LAND CRUSTACEANS. 83 



send two small branches into the abdomen, may be allowed to retain it. The sternal 

 artery, in its vertical course, that is before its bifurcation, gives off two or three small 

 branches backwards towards the abdomen. The ventral thoracic artery (7, fig. 19) gives off 

 branches right and left to the third, second and first pairs of legs and then bifurcates 

 into two trunks, one for each side, which supply the mouth-limbs and send a branch to 

 the green gland of each side. The ventral abdominal artery (8, fig. 19), in its course 

 through the hinder part of the thorax gives off vessels to the last two legs and then, on 

 arriving at the base of the abdomen, divides into two small branches, which ramify among 

 the abdominal organs. In the possession of these two little vessels, and in the greater 

 regularity of the arrangement of vessels to the limbs, the sternal arterial system of Goenobita 

 differs from that of Eupagurus described by Bouvier'. 



The abdominal artery (9, fig. 19). For a short distance this great vessel runs a straight 

 course backwards, giving off a few small twigs to the muscles of the hinder part of the 

 thorax. But a little behind the junction of thorax and abdomen it divides into two 

 branches. Of these one, the smaller (10, fig. 19), passes on in the middle line above the 

 hind-gut, lessening as it goes by giving off small vessels to the gut and ovary. The 

 larger of the two, however, turns downwards and then backwards again, and continues its 

 course below the liver and above the broad band of muscle which represents, in the 

 Pagurinea, the abdominal muscular system of other Decapods^ As it goes, this ves.sel 

 gives off branches upwards to the liver and testis and downwards to the muscles. In 

 particular one large branch, given off not long after it resumes the backward direction, 

 supplies much of the muscle-band and even sends a branch forward into the thorax. 

 Further back still, the main vessel divides into two. One division passes into the muscles, 

 the other runs on dorsal to the muscle-band, continuing to supply it and the liver. The 

 sub-muscular division reappears at the hind end of the abdomen and curves forward, 

 breaking up and anastomosing with the other vessels of the liver. 



Venous system. The arteries, after dividing into finer and finer branches, end by dis- 

 charging their blood into the great venous sinuses in which all the organs of the body 

 are bathed. The arrangement of these in Goenobita seems to be much the same as in 

 other Decapods. In connection with the respiratory organs, however, certain peculiarities 

 must be noticed. Roughly speaking, the blood from a sternal sinus passes to the gills 

 and so to the pericardium, that from a gastric sinus to the branchiostegite and so to the 

 pericardium, and that from an abdominal sinus to a plexus under the skin of the abdomen 

 and thence by two veins on each side to the pericardium. Some further particulars will 

 be found in the next section. 



iv. Respiratory Organs. Respiration takes place in three distinct regions of the 

 body of a Goenobita : (1) in the gills, (2) in the lining of the branchiostegite, (3) in the 

 abdominal skin. It must, of course, be borne in mind that in this case the surrounding 

 medium is not water, as with the great majority of Decapods, but air. 



The gills are of the type known as " phyllobranch " ; that is to say they consist of 

 an axis bearing on each side a series of thin-walled plates through which the blood flows 



1 Bouvier, "Bteherches anatomiques sur le Syst^me p. 197 (1891). 

 Artferiel des Crustac^s Decapodes." Ann. Set. Nat. (7), v. - See above, p. 69. 



11—2 



