178 EXPERIMENTS. 



he had covered with opaque varnish, might almost, for 

 instance, be quoted to prove the same with reference 

 to the compound eyes. "Mes Camponotus aux yeux 

 vernis," he says, "attaquaient et tuaient aussitot une 

 Formica fusca mise au milieu d'eux, la saisissaient 

 presque aussi adroitement que ceux qui avaient leurs 

 yeux. lis demenageaient un tas de larves d'un coin 

 de leur recipient a I'autre avec autant de precision 

 qu' avec leurs yeux." * 



On the other hand, Forel goes so far as to say that 

 if the compound eyes are covered with black varnish, 

 insects cannot even perceive light ("Cela prouve 

 qu'elles ne voyaient plus meme la lueur"). In fact, 

 the use of the ocelli seems a great enigma, at least 

 when the compound eyes are present. 



We must remember that some other Articulata — 

 spiders, for instance — possess ocelli only, and they 

 certainly see, though not probably very well. 



Plateau has made some ingenious observations, from 

 which it appears that spiders are very short-sighted, 

 and have little power of appreciating form. He found 

 they were easily deceived by artificial flies of most 

 inartistic construction; and he concludes that even 

 hunting spiders do not perceive their prey at a greater 

 distance than ten centimetres (about four inches), and 

 in most cases even less. Scorpions appeared scarcely 

 to see beyond their own pincers. 



I have also made some experiments on this point 

 with spiders (Lyeosa saccata). In this species, which is 

 very common, the female, after laying her eggs, collects 

 them into a ball, which she surrounds with a silken 

 envelope and carries about with her. I captured a 



♦ Becueil Zool. Suisse, 1887. 



