DIVISIONS OF THE HYDROZOA. 69 - 
corresponds to the clapper of the bell, and is termed the 
“manubrium” (Lat. for handle). From the fixed or proxi- 
mal extremity of the central process or manubrium proceed 
four canals, which extend to the margin of the bell, where 
they all open into a circular canal surrounding the mouth 
of the bell. This bell-shaped reproductive bud may attain no 
higher development than this, and may remain permanently 
attached to the parent organism from which it is produced. 
In other cases, however, a higher state of development is 
reached (fig. 19, @). The generative bud or gonophore 
becomes detached from its parent colony; the manubrium 
or central process develops a mouth at its free or distal 
extremity ; the mouth of the bell becomes partially closed 
by an inward prolongation or shelf, called the “veil;” and 
a series of tentacles are developed from its margin. The 
generative bud, thus liberated, leads a wholly independent 
existence. The manubrium, having developed a mouth, as- 
Fig. 19.—Generative buds or gonophores of the Hyarozoa diagramatically repre- 
sented. a@ Simple gonophore, consisting merely of a protuberance of the ecto- 
derm and endoderm; c Gonophore which has the structure of a Medusa 
(medusoid), but is not detached: d@ Free medusiform gonophore. 
sumes the functions of a true polypite, and its cavity acts as a 
digestive sac. The whole organism swims about freely, and 
has the power of assimilating food, and thus of attaining to a 
comparatively gigantic size. This independent existence, how- 
ever, only goes on till such time as the elements of reproduc- 
tion can be produced. The ova and sperm-cells are developed 
in specialised portions of this generative bud, and then it ceases 
to exist. The ova, however, when fertilised, do not develop 
themselves into the free-swimming bell-shaped organisms in 
which they were actually produced, but into the plant-like, 
rooted, and compound zoophyte, from which the generative 
buds were originally given forth. These free-swimming bell- 
shaped reproductive buds or gonophores, as we shall see, are 
