AJ^D PHYSIOLOGY OP THE SPONGIAD^. 
821 
by independent growth, or by spontaneous division of the sarcodous substance of the 
sponge. 
Both these modes of propagation occur in the same species, Spongilla fluviatilis, but 
I have never yet seen them both well developed in the same individual. Where the 
ovaria were abundant, the sarcode appeared even and consistent in its structure ; and, on 
the contrary, if it exhibited manifest symptoms of granulating, very few or none of the 
ovaria could be detected. This double means of propagation is by no means uncommon 
among the Zoophytes. 
I have never seen the spontaneous granulation of the sarcode in any living marine 
species of sponge ; but as the vital powers and general physiological characters of that 
substance appear to be the same in all the Spongiadse, however varied in form and 
structure, it is highly probable that perpetuation by spontaneous or accidental separa- 
tion of minute masses of sarcode is by no means confined to Spongilla, and that, from 
the concurrent testimony of all who have investigated the subject, every molecule of 
sarcode, however minute, has inherent vitality, and the power of uniting with its own 
congeners whenever they may chance to come in contact. 
Growth and Development of Sponges. 
The growth of the sponge does not appear to be continuous, but periodical, as we 
may observe in the branching species, and especially in H. palmata. If the sponge be 
held up between the eye and a lighted candle, as many as five or six of the former 
pointed terminations of the sponge in succession, from near the base to the apex, may 
be seen ; and the former lateral boundaries are also equally distinct, the oscula being 
most frequently, but not always, continued through the new coating of the lateral deve- 
lopment of the spongeous structure. New branches are also frequently thrown out 
during the last period of development at various parts of the stem where no indication 
of branches existed previously. In all these newly-developed parts, it may be observed 
that the primary lines of the structure of the skeleton, or those radiating at nearly right 
angles to the axis of the sponge, are those which are first developed; and at the extreme 
points of the branches they are frequently seen projecting for, comparatively, a con- 
siderable distance in the form of single unsupported threads or filaments ; but as we 
trace these lines inward, we find the secondary or connecting fibres increasing in num- 
ber, and the network becoming closer and more fully developed. The same mode of 
development may be traced in nalichondria oculata, Johnston, but not to such an 
extent as in H. palmata., Johnston, In the sessile massive species of Halichondroid 
sponges the same mode of development seems to obtain, as I have frequently traced the 
different stages of growth in sections at right angles to the surface of the sponge. 
5 T 2 
