COMPARATIVE MORPHOLOGY OF THE GALEODID^,. 365 



IX. The Heart and the Circulation. 



The Dorsal Vessel. — The dorsal vessel, or heart, of Galeodes is a long tube extending; 

 from about the 4th or 5th segment anteriorly to the 13th posteriorly. It is extremely 

 delicate, and, for the size of the animal, unimportant, this fact being attributed, according 

 to the well-known principle, to the great development of the tracheal respiratory 

 system. 



In spite, however, of tliis feeble development of the dorsal vessel in Galeodes, it 

 has retained certain primitive featui-es, viz., great length and a great number of ostia, 

 viz. eiglit pairs — two in the cephalothorax and six in the abdomen. These ostia, in 

 the abdomen at least, are strictly segmental and occur under the posterior third of 

 each tergite (PI. XXX. fig, 15), just in front of the dorso-ventral muscles. The 

 longitudinal section of the last chamber of a heart of a Bhax whose alimentary canal 

 was empty, and the abdomen consequently somewhat telescoped together, is given on 

 PI. XXXIV. fig. G. 



In addition to these eight pairs, there appear also to be indications, viz., a swelling of 

 the aorta, of an extra chamber anteriorly (PI. XXXI. fig. 5, h), which would imply that 

 there were originally at least three pairs of ostia in the cephalothorax. 



The ostia are on the dorso-lateral surface of the heart, and the valves are formed by 

 fine membranes attached posteriorly to the lips of the ostia and floating forwards on the 

 blood-stream. The lower membrane (or edge of the valve-tube) is attached anteriorly 

 to the floor of the chamber (PL XXXIV. fig. 6). On contraction of the heart, these 

 membranes would be forced up against the dorsal surface of the lumen and the aperture 

 would be closed. 



The anterior end of the heart is produced into an aorta, which rims through the mass 

 of tubules developed at certain times (? or in diff'erent S2:)ecies) by the proximal ends of 

 the coxal glands, and apiiears to discharge the blood direct on to the central nerve-mass 

 (PI. XXXI. fig. 5). 



The posterior opening of the heart, Avhich is valvular, the valve being formed by a 

 simple membranous infolding of the walls (PI. XXXIV. fig. 6), is immediately in front 

 of the stercoral pocket. The heart is continued into a vein, which appears to end just 

 behind the stercoral pocket. In transverse sections, the heart is seen to be suspended 

 by strands of connective tissue which, dorsally and dorso-laterally, are attached to the 

 body-wall, 1)ut ventrally radiate outwards on each side into i-egular wing-like arrangements 

 of strands, Avhich lose themselves among the digestive tubules (PI. XXXIV. fig. 8). 

 These wing-like strands may act as elastic expanders of the chambers of the heart ; 

 their chief function is, however, almost certainly to keep the heart from being too 

 compressed when the abdomen is tightly distended with food. 



Suspended on these strands and scattered about all around the heart large cells are 

 fomid, the function of which I have not ascertained; they may be connective-tissue 

 cells specialized as reserve cells, and suggest an incipient fat body, such as is found on 

 each side of the heart in many Hexapoda. The heart itself is very delicate, and consists 

 of but a single layer (ca. 6/* thick) of striated muscles lined on the inner side by a fine 



