OF THE SPONGIAD^E. 89 



tissues with the addition of nucleated cells immersed in the 

 sarcode. In the sponges of commerce it is exceedingly 

 largely developed, and nothing can be more different in 

 character than their soft and flexible skeletons and the 

 animal in its natural condition. Specimens of it in this 

 state, which have been preserved in spirit immediately on 

 being taken from the sea, have the whole of their interior 

 nearly as solid and firm as a piece of animal liver ; the 

 colour being a very light grey, or nearly white. While the 

 sponge, as a whole, is sensitive and amenable to disturbing 

 causes, the sarcode does not appear to be especially so, as I 

 have frequently observed a minute parasitical annelid which 

 infests the interior of Spotigilla fuviatilis, passing rapidly 

 over the sarcodous surfaces, and biting pieces out of its 

 substance without apparently creating the slightest sensa- 

 tion to the sarcode, or at all interfering with the general 

 action of the internal organs of the sponge; and in many 

 cases we find foraminiferous and other minute creatures 

 permanently located in its large cavities without appearing 

 to cause it the slightest inconvenience. 



O 



When separated from the living sponge, it has at certain 

 periods an inherent power of locomotion ; small detached 

 masses of it may be observed slowly but continuously 

 changing their form, and occasionally progressing in different 

 directions ; and Carter, in his valuable ' History of the 

 Freshwater Sponges of Bombay,' describes such detached 

 masses of sarcode, when progressing and encountering a 

 fixed point, as dividing longitudinally to avoid the impedi- 

 ment, and again uniting when it has been passed. This 

 gliding motion appears to be dependent on an inherent 

 contractile power, as no cilia appear to have been detected 

 on the surface of such locomotive masses. Dujardin has 

 recorded similar movements in portions of the sarcodous 

 substance from specimens of his genus Halisarca (Hymenia- 

 cidon Dujardinii,} Bowerbank ; and similar observations 

 have been recorded by Lieberkuhn and other writers during 

 their observations of the Spongiadae. I have frequently, 

 at different seasons of the year, taken portions of the sarcode 

 from living and healthy specimens of Sponyilla, in which I 



