624. The Siphonophores. [ September, 
passing from a common junction directly to a circular tube. In 
the fully grown bell, however, two of these tubes diametrically 
opposite differ considerably from the other pair, and take, in their 
course from common junction to the rim of the necto-calyx, a 
peculiar turn or twist which I have represented in my drawing, 
At their junction with the “circular tube” in the rim of the bell 
lie two or three large lasso or stinging cells, which do not appear 
in a corresponding position in the other tubes; these cells have 
been regarded by some naturalists as the remnants of tentacles 
which never are found fully developed on the necto-calyxes. The 
portions of the bell in which the tubes with an abnormal course 
lie, are the same which send out the projections embracing the 
_axis, and interlocking in the dovetailed manner I have described 
above. 
I should not regard even a popular account of the necto-calyx 
complete, if it did not include a mention of two tubes ending 
blindly in the substance of the bell; these arise from the medial 
tube connecting the radial system with the stem cavity, and are 
known as the “mantle vessels.” They lie in the same plane as 
those two radial tubes which do not have any variation in their 
direct course to the circular vessel. One of these tubes may be 
the same as the tubular cavity of the covering scale., Many nat- 
uralists have supposed that the structure last mentioned cor- 
responds with one of the radial tubes of a swimming bell. I 
think that homology not a good one, but I consider the cavity of 
the covering scale is homologous with one of the “mantle 
tubes. 
The necto-calyxes never voluntarily separate from the stem, 
but when by any mishap they are broken off, they still retain 
power of motion and move aimlessly about in irregular circles, 
keeping up muscular action for a considerable time. Their inde- - 
pendent life, however, is very short, for since they are separated 
from the axis no nourishment can be supplied them. They are 
_ locomotive in their function, but rely upon the fluid which circu- 
_ lates in the stem for their support. When such is not supplied 
them they die. ; 
c. The Covering Scale.— All of the stem except that upon 
which the necto-calyxes are fastened, is’ protected, in Agalma, by 
structures known as covering scales or bracts. The German 
designation of these parts “ Deckstiicke,” is used by some English © 
and American naturalists. The covering scales are gelatinous, 
