MUSEUM OF COMPARATIVE ZOOLOGY. 239 



PLATE in. 



Fig. 1. Upper portion of a taster of Nanomia, showing the so-called oil globule 

 forming a protuberance on one side The tentacle is not represented 



Fig. 2. Four nectocalyces of Nanomia, showing their mode of fitting together. 

 The stem is shown through the sides of the " horns," or gelatinous 

 extensions of the nectocalyx. The sinuous tubes are the lateral chym- 

 iferous vessels. The radial tubes, which pass directly, without a sinu- 

 ous course, from the tube wb>'-b joins the system to the stem, are not 

 shown. 



Fig. 3. Ualopsis ocellata (side view). 



PLATE IV. 



Fig. 1. A fish {Seriola zonata) with Hydrichthys attached to its side and anal 

 region. 



Fig. 2. Single cluster of gonophores separated from attachment to the basal plate 

 by which the whole colony is united to the fish. The attachment is at 

 the lower end. Medusa buds in various stages of development are 

 shown at the ends of the lateral branches. Each attached colony has 

 a large number of bodies like Fig. 2 scattered irregularly on the basal 

 plate. The structure represented in Fig. 2 is described as the gono- 

 some of Hydrichthys. 



Fig. 3. Single filiform body of a Hydrichthys colony. 



Fig. 4. Section (optical) of a medusa bud of Hydrichthys. The two projections 

 on the left are the opposite tentacles, which have an internal cavity 

 communicating with radial tubes, two of which are represented. The 

 two spurs from this cavity which arise near the bases of the tentacles 

 are the beginnings of the circular canal. The large cavity at the centre 

 of the bell is the cavity of the proboscis. The slit-like cavity separated 

 from the cavity of the proboscis by the thick layer and the thin layer 

 which lines the former, is the future bell cavity. 



Fig. 5. Enlarged end of the filiform body of Hydrichthys, showing the orifice open 

 and a round mass (food ?) in its cavity. 



PLATE V. 



Fig. 1. Adult medusiform gonophore of Hydrichthys with four tentacles (side 

 view). This medusa was raised from the hydroid, and is supposed to 

 be not much younger than the adult. 



Fig. 2. An immature medusa of Hydrichthys found in the aquarium on the morn- 

 ing after capture. Raised from the Hydrichthys in countless num- 

 bers. (Side view.) 



Fig. 3. View of the last-mentioned from actinostomal region. This medusa is 

 a very little younger than Fig. 2, since the two stumpy tentacles have 

 not yet begun to appear. 



