MUSEUM OF COMPARATIVE ZOOLOGY. 227 
stumpy tentacles at its free extremity. Small lateral branches without me- 
dusa buds are not rare, especially near the free extremity of the main stem. 
They are small, however, and project but little from the main stem. 
The free extremity of the gonosome, or of the main stem of the same, is 
destitute of medusa buds, and, as has been said above, is without appendage. 
There are no tentacles about this terminal opening, and its rim is entire. 
Whether the terminal opening of the main stem serves as a mouth or not 
it is impossible for me to say. No food was found in the cavity of the stem, 
and it is supposed that the whole structure is dependent upon the tubes of the 
basal plate for its nutrition. The main stalk is not supposed to take in food 
from the surrounding water through the terminal orifice. 
The cluster of buds at the extremity of the lateral branches of the gonosome 
are the structures which give the color to the colony. They resemble the 
medusiform buds found in other Tubularian hydroids in their mode of attach- 
ment, their general structure, and their mode of growth, 
In addition to the botryoidal clusters of gonosomes there also arise from 
the basal plate by which the colony is fastened to the fish long flask-shaped 
bodies, recalling in their external form the tasters of the Siphonophores. 
These bodies (Plate IV. Figs. 3, 5), like the gonosomes, arise from the upper 
walls of the basal plate of tubes attached to the body of the fish. ‘Like the 
gonosomes they are numerous in the hydroid colony. The filiform bodies are 
elongated flask-shaped structures, of about uniform size throughout, arising 
from different points of attachment at the base from the gonosomes. They 
are, like the gonosomes, destitute of appendages, but they probably have an 
opening at the free extremity. The walls of the filiform bodies are composed 
of an outer thin and an inner thickened layer. There is a cavity within. 
The walls are dotted with pigment spots, which are especially numerous 
around the free extremity. In one of these filiform bodies there is a spherical 
mass, which resembles half-digested food. It is doubtful whether this mass 
is food. The free end of the filiform bodies is sometimes trumpet-shaped, 
but ordinarily rounded, the opening being concealed by the contraction of the 
lips. The bodies of the filiform structures move backwards and forwards on 
their attachments, and are sometimes spirally coiled in a single turn. They 
recall in general appearance the spiral zodids of Hydractinia and the tasters ot 
Siphonophora, but, unlike either of these structures, have an orifice at their 
freeend. They are thought to have close likenesses to the “central polyp” 
of Velella. 
Medusa. — At the extremity of each lateral branch or its subordinate divis- 
ion there is found a small cluster of buds, which is composed of meduse in 
all stages of growth. While attached to the branch, and before separation 
from it, these bodies take on all conditions of growth, from a simple hernia- 
like spherical bulb to a cylindrical body with two stumpy tentacles. No 
more than two tentacles are developed in the oldest attached medusa go- 
nophore which was studied. The course of the growth of the medusa of 
Hydrichthys from a hernia-like bud to a small medusa is in no respect 
