i88o 1882] EARTHWORMS 215 



sickly (probably with parasites) worms is thus hastened. I Letter 549 

 will add a few words to what I have said about these tracks. 

 Occasionally worms suffer from epidemics (of what nature I 

 know not) and die by the million on the surface of the 

 ground. Your ruby paper answers capitally, but I suspect 

 that it is only for dimming the light, and I know not how to 

 illuminate worms by the same intensity of light, and yet of a 

 colour which permits the actinic rays to pass. I have tried 

 drawing triangles of damp paper 1 through a small cylindrical 

 hole, as you suggested, and I can discover no source of error. 

 Nevertheless, I am becoming more doubtful about the intel- 

 ligence of worms. The worst job is that they will do their 

 work in a slovenly manner when kept in pots, 2 and I am 

 beyond measure perplexed to judge how far such observa- 

 tions are trustworthy. 



To E. Ray Lankester. Letter 550 



Mr. Lankester had written Oct. nth, iSSi, to thank Mr. Darwin for 

 the present of the Earthworm book. He asks whether Darwin knows 

 of " any experiments on the influence of sea-water on earthworms. I 

 have assumed that it is fatal to them. But there is a littoral species 

 (Pontodrilus of Perrier) found at Marseilles." Lankester adds, " It is 

 a great pleasure and source of pride to me to see my drawing of the 

 earthworm's alimentary canal figuring in your pages." 



Down, Oct. ijth [iSSi]. 



I have been much pleased and interested by your note. 

 I never actually tried sea-water, but I was very fond of 

 angling when a boy, and as I could not bear to see the worms 

 wriggling on the hook, I dipped them always first in salt 

 water, and this killed them very quickly. I remember, though 

 not very distinctly, seeing several earthworms dead on the beach 

 close to where a little brook entered, and I assumed that they 

 had been brought down by the brook, killed by the sea-water, 

 and cast on shore. With your skill and great knowledge, 

 I have no doubt that you will make out much new about the 

 anatomy of worms, whenever you take up the subject again. 



1 Triangles of paper were used in experiments to test the intelligence 

 of worms (loc. cit.^ p. 83). 

 3 Loc. tit., p. 75. 



