10 
formed, and at which the branch is fiually thrown off. 
the regularity of the process by which this is eflected, 
well defined sear left behind, and the central pith n 'j 
being exposed, there is but little doubt left on my 
that each branch is thrown oft" by a vital process, similar ' 
sloughing in animals, or the shedding ot leaves in tre e ’ 
and is not washed off accidentally by the sea. i hat v1 ’ • 
stout and rigid species the Sertularia nigra is exposed to ^ 
same violence, rendered more effective by its rigidity, 
yet is not liable to have its pinnaj destroyed in a sifflj 
manner; ancl it is not unfrequently the case that in this 
species the pinnae are lorn or twisted off at various lengl * ’ 
hut such cases are not at all like the loss in the Ih. fW 
or T. articulata. The terminations of the stem and pin 0 { 
are said to be open, during growth, which, however, does 11 
appear to be the case ; but if care be not taken to k® j 
the specimens healthfully alive, or if they should bo pla c ^ 
in fresh water, these parts from being young and delicat® ^ 
formed, readily rupture and the granular pulp is for c ^, 
through the apertures. To such an extent is this someth 11 ^ 
the case, that through the whole polypidom scarce!) 
trace of the pulp remains. This seems to arise from 1 
irritability of the horny sheath, for that it is irritable th fi 
is suflicient proof. . 
There is an opinion entertained by some physiology 
that the external horny sheath is extravascular and cO 
sequently not endowed with vitality. It is considered 
them as an exudation from the granular pulp. To 
however, my observations do not enable me to agree. T& 
mode of growth, the formation of their celis, and » 
manner in which they cast their branches tend aga'^ 
such a conclusion. In the formation of the cells, , 
apertures are always closed at first, and the polypes j, 
developed before they are opened; the polypes, in 
enclosed state, do not press against the upper part ot [ 
horny covering, but lie towards the centre ol the cell. 
the upper portion gets thinner and finally opens about j 
middle and falls in, in the form of a funnel. 11 this P.^ 
was ruptured by the pressure from within, the torn ntai'o ^ 
would have been forced outwards, rather than have 1>e 9 
inverted as is always the case. This mode of op en *^°Ji 
cell is nearly alike in all the genera , yet they all after*' |j 
assume their specific differences — difierences so remark‘d 
and constant as to leave no doubt but that they are ^ 
result rather of specific actions than of an accident, 
peduncles of the cells of the Campanularice are naturally t ,) 
ringed at intervals, yet the animal possess a P ov ^ er j (1 e s 
corrugate them throughout their whole extent, and ^ 
it at one time and not at another. When the extreif 1 
