398 Dr. Sharp's account of recent experiments 



[The latter part of this thesis I do not think is 

 estabHshed by the investigations. — D. S.] 



2. As was supposed by Cornaha, Landois, and Maurice 

 Girard, the Umit of distinct vision is short ; according 

 to my observations it is generally about a centimetre 



(t in.). 



3. At greater distances caterpillars can perceive the 

 existence of large objects, but they do not distinguish 

 their nature ; they no longer see, using the word in an 

 exact sense, 



4. They do not perceive movements of objects in their 

 neighbourhood at a greater distance than their limit of 

 distinct vision. 



5. Many caterpillars that are more or less pubescent 

 bear, on the first segments, tactile setse, by which they 

 are immediately warned of the presence of objects when 

 these are touched by the setse. 



6. All caterpillars make constant use of their antennee 

 for exploring the surface of the object they are moving 

 on, and that of such bodies as they may meet during 

 their advance. 



The next subject treated by Prof. Plateau is one that 

 has been previously much discussed, viz., the function of 

 the ocelli of perfect insects. 



He proceeded by obscuring the ocelli and compound 

 eyes, 1 alternately, 2 conjointly, and then observing to 

 what extent the movements of the insects were effected. 

 The modes used for obscuring the optical organs were 

 also two in number — 1st, and chiefly, by covering the 

 ocelli or compound eyes with a mixture of oil and black 

 pigment ; 2nd, by severing the nerves of the organs by 

 means of a cataract-knife. 



[As regards this part of Prof. Plateau's subject, I 

 would remark that I think the question discussed is 

 psychologically considerably more complex than those 

 who have written on the subject have perceived. A first 

 objection strikes one : it is that the function of the optic 

 organs generally being doubtful, or at least very ill- 

 known, it is not probable that the more special question 

 as to what is the particular function of the ocelli can be 

 satisfactorily dealt with. To this may be added a 

 second criticism, that the methods of observation that 

 have been used bear only on the question as to what 



