AND PHYSIOLOGY OF THE SPONGIADiE. 
775 
The spinulo-recurvo-quaternate spiculum, the growth and development of which I 
have described in the first part of this paper (Phil. Trans. 1858, p. 293), presents an 
admirable illustration of the combined defensive and aggressive character of some of 
these internal defensive spicula. The sponge in which they occur belongs to the Hali- 
chondroid tribe, the skeleton being composed of a network of spicula cemented together 
by their apices, which cross each other at the angles of the areas of the reticulations. 
The recurvo-quaternate spicula are not dispersed on all parts of the skeleton, but are 
congregated in groups, frequently consisting of as many as fifteen spicula, the whole of 
their bases being concentrated on one of the angles of the reticulations of the skeleton, 
while their shafts and apices radiate thence in every direction into the interstitial spaces 
of the sponge ; they are thus placed on the strongest and most elastic portion of the 
skeleton, with their hemispherical bases firmly imbedded in the cementing keratode of 
the skeleton, which abounds at the angles of the network, and which by its inherent 
elasticity and strength renders the insertion of the base of the spiculum, in strength and 
extent of action, quite equivalent to the powers of the ball-and-socket joints in the higher 
tribes of animals. A small annelid or other minute intruder entangled amidst these 
numerous sharp hooks would struggle hopelessly in such a situation, as the spicula, from 
the nature of their attachment, would yield readily to its struggles in every possible 
direction, and at every new contortion arising from its efforts to escape it would inevitably 
receive a fresh series of punctures and lacerations. 
Fig. 10, Plate XXX. represents a small portion of the skeleton of the sponge bearing 
the spinulo-recurvo-quaternate spicula in situ. 
In other instances, where defence alone appears to be contemplated, we do not fin d 
these beautiful adaptations for motion in every direction prevail. The bases of the 
spicula in those cases are abundantly spinous, and are evidently intended to maintain a 
firm hold by their attachments, and are destined rather to rigidly maintain their position 
than to yield to any struggling body with which they may be in contact. The numerous 
spines with which these shafts are frequently covered are calculated to wound and lace- 
rate, rather than to retain the enemies with which they are engaged*. 
* Since I wrote the first portion of this paper, I have received from my friend, Mr. J. Yate Joexsox, of 
Madeira, a new and very illustrative instance of the combination of defence and aggression in the structure 
and offices of the internal defensive spicula ; and in this case it is not a new organ, but an adaptation of a 
well-known form to a new purpose, in the shape of a contort trenchant bihamate spiculum of unusual size and 
structure. In the course of my examination of the results of the deep-sea soundings in the Atlantic, I found 
several of these spicula, and was much interested by the singularity of their structure, which at that time I 
could not comprehend. 
The general outline is much like that of the type-form so commonly found imbedded in the sarcode, but 
it is somewhat less flexuous in its curves, and the shaft and hami are very much larger and stouter than 
those of the spicula of the sarcode. But the most singular point in their structure is, that while the curved 
portion of the hami and the middle of the shaft are perfectly cylindrical, the inner portion of the hooks and 
those parts of the shaft immediately opposed to them present sharp trenchant edges, so that each hook 
assumes to some extent the form of spring hand-shears. The acute termination of the hook and the opposed 
trenchant edges exhibit every facility for effecting an entrance through the tough skin of the victim, while 
