390 REPORT—1868. 
for example, in Corymorpha and certain allied forms, and apparently also in 
the curious free trophosome of Nemopsis, as described by M*Crady, and of 
Acaulis, as described by Stimpson*, 
Polypite-bud in the Tubularida.—When a polypite-bud is about to become 
developed from any part of the ccenosare in the Tubularida, the two layers of 
the ccenosare are seen at this spot to be pushed outwards as if by an incipient 
hernia, and the little hollow tubercle thus produced forces before it the in- 
vesting periderm, which is first extended over the advancing bud, and is at 
last absorbed or ruptured, 
The little bud, however, has been in the mean time clothing itself with a 
new periderm, which, now that it has escaped from the confinement of the old 
one, is seen to cover it with a very delicate, transparent, structureless pel- 
licle. The bud continues to increase in size, becoming longer and thicker, 
with its endoderm and ectoderm very distinct, and with its cavity opening 
freely into that of the branch from which it springs, and admitting into its 
interior the fluid with the floating granules, which fill the general cavity of 
the ccenosare, and which are kept in a state of active rotation within the bud. 
It continues to enlarge, but has its distal extremity still closed, while the 
entire bud is still invested by its delicate periderm. 
We next find that the little bud has acquired a somewhat clavate form by 
the enlargement of its distal extremity. While the periderm which clothes 
the growing bud continues, by means of new layers deposited upon its inner 
surface, to increase in thickness over the whole bud, except at its extremity, 
these new layers cease, in almost every case, at avery early period to be 
excreted from the free extremity of the bud, and the periderm here accord- 
ingly remains in the condition of a transparent structureless pellicle, of ex- 
treme tenuity, in which state it may often be found in the fully developed 
polypite, though it is also frequently impossible to demonstrate its presence 
after the polypite has attained its complete form. 
Whether this delicate continuation of the periderm remains through the 
life of the polypite or entirely disappears at an early period, we now find 
tentacles begin to grow out from the enlarged extremity of the bud, and a 
terminal mouth to become developed; the form is thus gradually assumed 
which is to characterize the adult polypite. 
In some cases, however (Coryne vaginata, Hincks, and Eudendriwm vagi- 
natum, Allm.), the periderm which clothes the free extremity of the growing 
branch attains considerable thickness, and does not disappear until a later 
period ; but it ceases in such cases to be in close contact with the ectoderm, 
and the polypite continues to become developed within an outer chitinous 
capsule ; and this development proceeds to the formation of tentacles and the 
assumption, more or less, of the adult form by the polypite-bud, before the 
rupture of the enclosing capsule places the young polypite in direct relation 
with the surrounding water +. 
The development of the polypite-bud in Hyd7a seems to be, in all essential 
points, the same as in the Tubularida, the most important differences being 
those which depend on the absence of a periderm in Hydra. The ultimate 
destination of the bud, however, is very different in the two cases; for while 
* It seems to me, however, still a question whether the free hydroids described by the 
American observers as Nemopsis and Acaulis be not the detached polypites of a fixed 
Tubularidan which may possess the habit of throwing off its polypite-heads, as we know 
to be the case in certain European species of Tubularia. (See below, p. 391.) 
+ A very unusual condition is presented by Bimeria nutans, Wright, in which the 
periderm is continued as a thick closely investing tunic over the whole of the polypite, 
except the tips of the tentacles and a small space just behind the mouth. 
