336 PRE-DETERMINATION IN NATURE 



necessaiy to fit them for vision in air, the compound eye in 

 insects, the simple eye in Batrachians. 1 The original photo- 

 graphic cameras, strange though this may appear to us, were 

 intended for use under water ; but at a very early time they were 

 adapted to work in air. 



But we must bear in mind that this early solving of advanced 

 problems in mechanics, optics and physiology was in favour of 

 Crustaceans and cuttles, which were lords of creation in their 

 time. There were in those early days humbler creatures whose 

 structures also present wonderful contrivances. 



I have already referred, in the chapter on imperfection of the 

 geological record, to the fossil sponges which have been found 

 in so great number and perfection in some of the oldest rocks 

 of Canada, and which have for the first time enabled us to 

 appreciate the forms and structures of the wonderful silicious 

 sponges which preceded those with which the dredgings of the 

 Challenger\\a.vQ made us familiar in the modern seas. Humble 

 sarcodous animals, without distinct muscular or nervous 

 system or external senses, the sponges have at least to live and 

 grow, and to that end they must already, in the dawn of life on 

 our planet, 2 have perfected those arrangements of ciliated cells 

 in chambers and canals which the microscope shows us driv- 

 ing currents of water through the modern sponges, and thereby 

 bringing to them the materials of food and means of respira- 

 tion. It is true we know as little as the sponges themselves of 

 the modus operandi of those perpetually waving threads which 

 we call cilia or flagella, yet they must have existed with all their 

 powers even before the Cambrian period. 3 



1 See ante, chapter on Air-breathers. 



2 I have found spicules of sponges in the chert nodules from the Huronian 

 limestones of Canada. 



3 Many species of hexaclinelled sponges have have been described from 

 the upper Cambrian or lower Cambro-Silurian of Canada. See paper by 

 the author in the Transactions of the Royal Society of Canada, 1889. 



