272 HAECKEL 



As there is an enormous number of different 

 sponges, he had confined his studies from the 

 first to a single group of them that might be 

 taken as typical. He chose the calcispongiae (cal- 

 careous sponges), which had been the least studied 

 up to that time. As the name obviously implies, 

 these sponges form their internal framework or 

 skeleton, not of elastic horny fibres like the 

 common bath-sponge, but of solid calcareous 

 needles or spines. They secrete these out of the 

 soft substance of their bodies just as the radio- 

 laria do their pretty siliceous houses. Haeckel 

 was engaged for five years, from 1867 to 1872, in 

 a profound and careful study of the natural his- 

 tory of the calcispongiae. Then he published the 

 results in his Monograph on the Calcispongice, 

 consisting of two volumes of text and an atlas of 

 sixty fine plates. 



The first result was that the calcispongiae 

 afforded a splendid proof of the impossibility of 

 drawing sharp limits between species in the per- 

 petually developing animal world. In their case 

 the different varieties passed constantly out of 

 each other and back into each other in a way 

 that would have made a classifier of the old type 

 distracted. But Haeckel had travelled far beyond 

 the position of his boyhood, when he had timor- 

 ously concealed the bad species that would not 

 fit into the system. He said humorously that in 

 the case of the calcispongiae you had the choice 

 of distinguishing one genus with three species, or 

 three genera with 239 species, or 113 genera with 



