ACCIDENTAL QUALITIES 187 



oxidises and gives out light and so these organisms are 

 " phosphorescent " without any consequence, good or bad, 

 to themselves. And then we come upon others (as, for 

 instance, the glow-worms and fire-flies) which have made 

 use of this " accidental " quality, and produce phosphores- 

 cent light in special organs so as to attract the opposite 

 sex. Again, we find that the red-coloured oxygen-seizing 

 crystalline substance haemoglobin exists in the blood of a 

 vast number of animals, and might as well be green or 

 colourless for all the good its colour does them. Yet here 

 and there the splendid red colour which this chemical 

 gives to the blood becomes of great importance as a "decora- 

 tion," or "sex-ornament." The comb of the domestic fowl, 

 the wattles of the turkey, but above all the supreme beauty 

 of the human race the cherry-red lips and the crimson- 

 blushing cheek of healthy youth owe their wonderful 

 colour to the red blood which flows through them. So at 

 last the redness of the oxygen-carrier is turned to account. 

 So it must be also with odorous substances. Many have 

 been called into existence, but few have been chosen in the 

 long course of animal evolution and selected as the impor- 

 tant means of repulsion or attraction. 



There are odorous substances attached to many of 

 the lower animals which seem to have no significance, 

 but just happen to be the result of necessary chemical 

 changes, not aimed (so to speak) at their production. Of 

 course, it is very difficult to form a certain and definite 

 conclusion as to their uselessness as odours. For in- 

 stance, nearly all the sponges when fresh and filled with 

 living protoplasm have a curious smell which reminds 

 one of that given off by a stick of phosphorus. Marine 

 sponges have it, and so has the beautiful green or flesh- 

 coloured river sponge (common on the wood of rafts 

 and weirs in the Thames). A rather uncommon marine 

 worm, called Balanoglossus, or the acorn worm, has a very 



