244, ARTHUR E. SHIPLEY. 
was 19:08 grms., that of the sand 10:03 grms. In two of 
them the sand weighed more than one half the total weight, 
the body being in one case 24°4 grms. and the sand 13°72, and 
in the other 15:05 grms. and 9:45. The contents of the 
intestine consisted of blackish sand with a few Foraminifera 
mixed with it. In spite of the considerable amount of sand 
which these figures show to be contained in the intestine, the 
wall of this tube in all the Sipunculids with which I am 
acquainted is excessively thin, and apparently but poorly 
adapted to retain the sharp and jagged pieces of sand which lie 
within it. A similar tenuity of the wall of the alimentary 
canal also occurs in Hchinids and Holothurians. Although 
this wall is so thin I have never found a Sipunculid with its 
intestine ruptured, so that in spite of appearances it seems to 
serve its purpose well. 
I have mentioned above that I am of opinion that the 
respiration of Onchnesoma is carried on through the walls of 
the intestine. The seat of the process of respiration 1s still a 
debatable point in the anatomy of the unarmed Gephyrea. 
Of the two recent authors who have written on the anatomy 
of Sipunculus, Mr. Andrews! is convinced that the tentacles 
act as branchie, whilst Mr. Ward? is of opinion that they do 
not. In Onchnesoma, at any rate, there cannot be any 
question as to the respiratory action of the tentacles, as the 
latter are entirely absent. In other Sipunculids the tentacles 
may to a slight extent serve as the organs of respiration, but 
the closed vascular system which supplies them with blood is 
of such a very limited extent that it would ouly suffice for a 
small portion of the body ; on the other hand, it seems to me 
quite possible that the brain, which is almost entirely sur- 
rounded by this system, may obtain its oxygen from it. 
The chief circulating medium in the body of the unarmed 
Gephyrea is undoubtedly the corpusculated coelomic fluid, and 
1 Loe cit., p. 419. 
2 «Onsome Points in the Anatomy of Sipunculus nudus, L.,” Henry B. 
Ward, ‘Bull. of the Museum of Comp. Auat., Harvard College,’ vol, xxi, 
No. 3, May, 1891. 
