66 



POPULAR ILLUSTRATIONS OF 



other things, it uses as weapons of defence. Now, the first thing 

 that the little Sponge does after it has become fixed to the rock, is to 

 begin to manufacture these spiculae, and it so arranges them that 

 any animal coming full tilt to make a mouthful stands a fair chance 

 of being impaled on their spear-like points. Should the assailant, 

 worm-like, try to work its way through the outer defences, it finds 

 a masked chevaux de frise all pointing outwards beneath the external 

 covering of the Sponge. This matter of self-defence being provided 

 for, that of growth comes next. Again the spiculse are brought into 

 play, to act as supports to the proper texture of the animal that 



Figs. 82 (magnified 260 diam.) and 83 (magnified 160 diam.), sponge-spiculse of the skeleton. 



Fig. 84. Connecting spiculum (magnified 90 diam.). 



Fig. 85. Defensive spiculum (magnified 308 diam.), from 2200 fathoms, Indian Ocean. 



Fig. 86. Tension spiculum (magnified 660 diam ). 



Fig. 87. Retentive spiculum (magnified 400 diam.). 



which we know as Sponge, which scientific chemists call " keratode," 

 but which Grant very properly altered to "keratose," because, 

 although Sponge may appear like horny elastic fibre, it is not chemi- 

 cally or structurally allied to horn ; while, strange as it may appear, 

 it differs but very little in chemical constitution from silk. Well, 

 then, the spongy texture grows upwards, all its internal network and 

 canals being lined with a reproduction of the sarcode cell which con- 



