152 ANATOMY AND PHYSIOLOGY 



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 

 sabrftance appear to be the same in all the Spongiadae, how- 

 ever varied in form and structure, it is highly probable that 

 perpetuation by spontaneous or accidental separation of 

 minute masses of sarcode is by no means confined to 

 Spongilla ; and from the concurrent testimony of all who 

 have investigated the subject, that 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 con- 

 tinuous, but periodical, as we may observe in the branching 

 species, and especially in Isodictya pcdmata, Bowerbank. 

 If the sponge be held up between the eye and a lighted 

 candle, as many as five or six of the former pointed termi- 

 nations 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 development 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, compara- 

 tively, a considerable distance in the form of single unsup- 

 ported threads or filaments ; but as we trace these lines 

 inward, we find the secondary, or connecting fibres increas- 

 ing in number, and the network becoming closer and more 

 fully developed. The same mode of development may be 



