126 ANATOMY AND PHYSIOLOGY 



remarkable, and highly suggestive of a capability of adapta- 

 tion to circumstances that we should scarcely have expected 

 to find. By the two instinctive habits, first, that of con- 

 verting the plant into an artificial skeleton, and then 

 erecting its spinous spicula on its fibres, it at once simu- 

 lates the habits of a kerato-fibrous sponge, and becomes 

 capable of the carnivorous habits that I have attributed to 

 those sponges that are so strikingly adapted for preying on 

 intruding annelids or other such small creatures. In the 

 species above described, Hymeniaddon C/iftoni, Bowerbank, 

 MS., the erection of the spicula on the adopted skeleton is 

 an established habit ; and it may be said to be instinctive 

 in the species, but I have observed the same fact in sponges 

 not habitually parasitical. I have a specimen of Micro- 

 dona carnosa, Bowerbank, a British species, in my posses- 

 sion in which some small fibres of a tubular zoophyte have 

 been accidentally included during its growth, and which the 

 sponge has coated with its own tissues, and from these 

 adopted columns defensive spicula are projected in a similar 

 manner to those of the columnar skeleton of the sponge. 

 In this case we have an instinctive adaptation of an 

 extraneous substance in a sponge in which the introduction 

 of foreign substances is the exception, and not, as in other 

 tribes of sponges, the rule. 



In Hyalonema mirabilis, Gray, a sponge nearly related 

 to the genus Alct/oncellum, we find another extraordinary 

 series of internal defensive spicula, the structure of which 

 I have described at length under the head of " Defensive 

 Organs." These elaborately and wonderfully-formed weapons 

 are evidently destined for other purposes than that of simple 

 repulsion. The spiculated cruciform spicula, with their 

 short stout basal radii planted firmly on the lines of the 

 skeleton, and projecting from their centre at right angles 

 to their own plane ; the long spiculated ray furnished with 

 numerous strong sharp recurved spines, it will be at once 

 seen, is eminently fitted to retain annelids or other such 

 prey, and to cause every motion of the struggling victim to 

 contribute to its own laceration and destruction, while the 

 structure and mode of attachment of the cruciform base is 



