390 F. M. BALFOUR. 
which have been enumerated as common to the whole of 
these larvae are not such secondary characters as (in accord- 
ance with the considerations used above) might be expected 
to arise from the fact of their being subjected to nearly 
similar conditions of life. Their transparency is, no doubt, 
such a secondary character, and it is not impossible that 
I'm. 7 . — Three Stages in the development oj Antedon {Comatula). (From 
Lubbock, after Thompson.) A. Larva just batched. B. Larva with 
rudiment of the calareous plates. C. Pentacrinoid larva, 
