fHE COMING OF LIFE 17 



sense of smell; the chief means of recognition of food. 

 Tentacles form exquisite organs of touch and very possibly 

 of other senses. The cells with fine hairs, which we found 

 in ccelenterates are still abundant, and may be accessible to 

 a variety of stimuli. Little sacks lined with similar hairs, 

 otolith-vesicles, are probably organs of feeling delicate vibra- 

 tions in the water, and giving warning of the nearness of foe 

 or food. They are on the way to become organs of hearing. 



We have found the eye as a pigment speck in flat worms 

 and probably in primitive ccelenterates. In some of the flat 

 worms such pigment specks have sunk below the surface 

 and light is allowed to enter only along a single line of direc- 

 tion. The skin covering the aperture is transparent and if it 

 thickens gradually into the form of a lens, and the pigmented 

 surface becomes more delicately and fully innervated, we have 

 an organ which is no longer merely photoscopic, light per- 

 ceiving, but also eidoscopic, forming images of external ob- 

 jects. At least one annelid, alciope, has attained such a truly 

 visual eidoscopic eye giving an image of objects within a very 

 narrow range of vision. 



We cannot overestimate the importance of the development 

 of a visual eye. It may be crude and near-sighted, but " among 

 the blind, the one-eyed man is king." Among higher types 

 of animals an eye with some means of forming an image is 

 universal. Eyes, otolith vesicles or ears, tentacles and other 

 sense organs are all situated at the front end of a vigorous 

 cylindrical animal writhing its way through the water. Here 

 the watch and lookout for food and danger must be maintained. 

 All these sense-organs are innervated from the supra-oesoph- 

 ageal ganglion which is continually pelted with stimuli from 

 all sides and sources. It is growing fast but is hardly suf- 

 ficient for the work and demands thrown upon it. The an- 

 nelid can hardly be said to possess a true head and brain, but 

 if it keeps its front end foremost and does not drift it will 

 surely develop one. To adopt the expression of the stock- 

 market it is very " long in futures." 



These annelids, and probably others somewhat like them, 



