842 The Siphonophores. [ August, 
divisions, of which Agalma, Diphyes and Gleba are representa- 
tive genera. 
Gleba resembles the Physophore in possessing many swim- 
ming-bells, and the Diphye in being destitute of a float. Diphyi- 
zooids, if such exists, are unknown, and an opposite law from 
that which exists in Agalma is followed in the order of develop- 
ment of the nectocalyces on the nectostem. The group of Hip- 
popodiz contains the two genera Gleba and Vogtia. The Amer- 
ican representative is the genus Gleba, which is found in the 
Gulf Stream.’ Vogtia is probably the young of Gleba. The 
swimming-bells of Gleba are hoof-shaped structures and are 
arranged in two rows or series, the opposite members of which 
fit closely together. The resemblance in shape of each bell toa 
horse’s hoof is very striking. The upper portion of the hoof 
points downward and outward, and upon its face is found an 
opening, the bell orifice, into a shallow bell cavity. The lower 
surface is concave, and as the animal swims is uppermost in the 
water. The bell substance although gelatinous and transparent, 
is less flexible than that of most other Siphonophores. The bell 
walls have little or no power of contraction and expansion, and 
the bell approaches closely in structure the covering scales of 
several other Siphonophora. 
The velum of the swimming-bell has a crescentic shape, and by 
its strokes upon the water, rather than by the contractions of the 
bell walls, the medusa is driven from place to place. The shal- 
lowness of the bell cavity and the irregular shape of the bell 1t- 
self brings about a variation in the regular course of the tubes of 
the bell. One of the radial tubes of the bell is much larger thon 
the others, although all pass directly from a common he ” 
the circular marginal tube. This long tube is swollen midway 12 
its course into a flat disk-shaped cavity or enlargement of un- 
known function and homology. The somatocyst lies just below 
the floor of the concave face of the bell, opposite the bell e 
ing, and hasa tubular form. It closely resembles the cen s 
tube of the covering scales of Agalma. As it is probably homo 
ogous with the somatocyst of other Diphyæ, it gives us 4 pe 
the homology of the central tube of the covering ae de 
somatocysts, wherever found, are the same as the pets F 
. tubes” in Agalma. There are no true covering scales without! 
1 Bull. Mus. Comp. Zodl., 1x, 8. 
