48 
STRUCTURE AND PHYSIOLOGY 
The gemmules are all clothed with vibratile Fig . 6. 
cilia similar to those of the tentacula of the 
parents. Sometime previous to their dis- 
charge from the polypidom they are observ- 
ed to be in a constant rotatory motion, by 
which their birth seems to be facilitated ; and now at liberty in 
the water they move and swim about as if they were guided by 
volition and sense, whirling at the same time on their own axis.* 
This freedom to move whither they list may continue for several 
hours, or even for two or three days, before a proper site for 
their permanent stay and future growth is found, when they 
begin to shoot up rapidly into those beautiful forms particular 
to each species, as the Supreme Being has ordered and deter- 
mined. The transformation of the ova, says Dr Grant, 44 from 
their moving, irritable, and free condition of animalcules, to that 
of fixed and almost inert zoophytes, exhibits a new metamor- 
phosis in the animal kingdom, not less remarkable than that of 
many reptiles from their first aquatic condition, or that of insects 
from their larva state.” One purpose of this mobility in the 
ova is obvious ; — it is a means ordained for their diffusion, for 
the parents being fixed immoveably to one spot, the reproduc- 
tive germs would have dropt and sprung up at their roots, had 
they not, by some such mechanism as we have described, been 
carried to a distance, and spread over the bosom of the deep. 
The evolution of the gemmules, subsequent to their fixation, has 
been minutely traced by Professor Grant and Sir J. G. Dalyell. 
When the bud falls from the crested head of Tubularia indivi- 
sa, slight prominences, enlarged at the tips, pullulate from the 
under surface, and the 44 nascent animal” elevating itself on 
these rudiments of the tentacula, as on so many feet, enjoys the 
faculty of locomotion. 44 Apparently selecting a site, it reverses 
* In reference to those of Flustra carbasea — and the observation appears to 
be very generally applicable — Dr Grant says — “ they are very irritable, and are 
frequently observed to contract the circular margin of their broad extremity, and 
to stop suddenly in their course when swimming ; they swim with a gentle glid 
ing motion, often appear stationary, revolving rapidly round their long axis, with 
their broad end uppermost, and they bound straight forward, or in circles, with- 
out any other apparent object, than to keep themselves afloat till they find them- 
selves in a favourable situation for fixing and assuming the perfect state.” — Edin. 
New Phil. Journ. iii. 117. 
