•jus 



THE VOYAGE OF H.M.S. CHALLENGER. 



in another it is distinctly niue-lobed. A few Sponges, Polyzoa, &c., are attached in some 

 of the specimens to the left side. 



The following list shows the dimensions in twelve individuals of this species : — 



The test is moderately thick but very soft. The blood-vessels are large and 

 abundant, and are conspicuous on the inner surface of the left side. Their terminal 

 twigs in the outer layers have enlarged knob-like ends. Bladder cells are abundant ; they 

 are very large throughout the inner three-fourths of the thickness, but in the outer fourth 

 they become smaller and are more closely packed. The ordinary minute fusiform cells 

 are also present. The mantle is of moderate strength ; the musculature is irregular on 

 the right side of the body and the anterior half of the left, while it is absent on the 

 posterior half of the left, over the stomach and intestine. 



The branchial sac (PI. XXXI. figs. 5 and 6) is large, completely filling the mantle 

 cavity. It is slightly plicated longitudinally, and the stigmata are arranged in alternate 

 bands of narrower and wider ones corresponding with the crests and troughs of the 

 plications. The large transverse vessels are very wide, and are somewhat encroached 

 upon by the ends of the narrower stigmata. In figure 5, which shows the outer (atrial) 

 side of the branchial sac, one of the muscular suspensors or tubes (s.) connecting the 

 sac with the mantle is seen at the right hand lower corner. 



The dorsal lamina (PI. XXXI. fig. 7) is broad but delicate, and the edge is strongly 

 serrated ; it extends a little more than two-thirds of the way down to where the oesophageal 

 opening is placed. The tentacles (fig. 8, tn.) are filiform, and the longer ones are very long 

 and thin, running out to fine terminations. 



The nerve ganglion is oblong, of a yellow colour, and gives off two large nerves at 

 each end — one pair to the branchial and the other to the atrial aperture. 



The alimentary, genital, and renal viscera form a large but flat mass upon the 

 posterior half of the left side. The oesophageal aperture is situated near the posterior end 

 of the sac, and from it the oesophagus runs posteriorly and ventrally ; the large stomach 

 continues the curve, running ventrally and anteriorly, and then turns directly anteriorly ; 

 the intestine, after leaving the stomach, continues anteriorly, then bends dorsally for 

 a short distance, and then runs back again posteriorly, nearly parallel to the stomach ; 

 finally it bends forwards, and runs anteriorly and dorsally to end in a wide anus, a little 



1 This specimen was not perfect, it must have been of enormous size. 



