Mutations and Evolution. 
243 
The views here set forth regarding the occurrence of both 
mutational and adaptational characters in organisms are entirely 
in harmony with Dendy’s (1913, 1916) conclusions from 
investigations of the sponges. He concludes that the specific 
characters of sponges are generally non-adaptive, and that a great 
many of the spicule differences so characteristic of the group must 
have originated by mutations. He also points out what we would 
now regard as parallel mutations, as in the appearance of 
trichodragmata, and in the polyphyletic family Epipolasidas, which 
is an assemblage of stelletid sponges which have independently 
lost their trisene spicules. Usually the most minute differences, 
both in megascleres and microscleres, remain constant throughout 
the species, though millions of spicules may occur in each 
individual, to whom these microscopic differences cannot be of the 
slightest use. Such differences point to chemical or physical 
alterations in the constitution of the germplasm. 
On the other hand, adaptive modifications of spicules for 
various purposes have taken place, as in the modification 
of triaenes into grapnels for anchoring the sponge to a muddy 
bottom, or into discotriaenes which serve as a dermal protection. 
Some of these adaptive conditions may have come about through 
selection among a series of mutations, but it is difficult to see that 
any of them involve the principle of inheritance of acquired 
characters. 
