396 Dr. Sharp's account of recent experiments 



when it reflects much white Kght, or light belonging to 

 the more refrangible region of the spectrum. This per- 

 ception is probably in part dermatoptic. 



6. Myriopods do not perceive the form of objects. 



7. Some of them appear to perceive considerable 

 movements. 



Part II. 



The second portion of Professor Plateau's researches 

 is devoted to Arachnides (Araneides, Scorpionides, and 

 Phalangides). Spiders, it would appear, do not see their 

 prey well, if at all, and without giving details of the 

 experiments, it will be sufficient to give the learned 

 Professor's summary of their results (Part 11. , p. 35) : — 



1. Spiders in general perceive at some distance 

 changes of position of voluminous bodies. 



2. Hunting-spiders (Attides, Lycosides) are probably 

 the only ones that perceive the movements of small 

 objects. 



3. They perceive these movements at a distance 

 varying, according to the observers and to the species 

 observed, between f in. and 8 in.* (2 to 20 centimetres). 



4. The distance at which the prey is seen sufficiently 

 well for its capture to be attempted is only from f in. to 

 f in. 



5. Even at this slight distance vision is not definite, 

 since hunting spiders make numerous mistakes. 



6. Web-making spiders have a vision that at all 

 distances is contemptible ; they are only aware of the 

 presence and position of their prey by the vibrations of 

 their snares, and endeavour to catch objects quite dis- 

 similar from insects when these objects cause shocks and 

 vibrations in the webs similar to what would arise from 

 the movements of winged Arthropods. 



Part III. 



In the third memoir Plateau passes to the true Insecta, 

 but still confines his observations to the functions of 

 simple eyes : this part of his memoir consists of two 

 distinct portions, viz., a, vision in caterpillars; b, the 

 function of frontal ocelli in perfect insects. 



■■= In a note Prof. Plateau says tliat he thinks this limit should 

 be reduced to 44 in. 



