156 VIGNETTES FROM INVISIBLE LIFE. 



form seen in the seed ; the other the needle sort, 

 investing the external tissue. In hoth cases they 

 are formed of silex, and of very simple construc- 

 tion. There are, however, many forms of spicula 

 in the great Sponge family ; and commencing with 

 the lowly form now before us, we might trace their 

 development in endless diversity, from simple needle, 

 or thornlike bodies, up to their marvellous develop- 

 ment and complexity of arrangement in the beauti- 

 ful EuplecteUa, or Yenus's flower-basket, of the 

 Manilla seas, which forms so prominent an object 

 of beauty in our own homes. 



