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 unifor-m 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 zooids of Hydractinia and the tasters ot 

 Siphonophora, but, unlike either of these structures, have an orifice at their 

 free end. 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 medusae 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 



