774 SCIENTIFIC RECORD FOR 1885. 



ropods have a shorter body than in after life, and the first three seg- 

 ments bear but a single pair of legs. 



In adult life, these first three segments still bear but a single pair of 

 limbs, while all the other segments which exist in the larval state, and 

 those which develop afterwards, bear two pairs. The Chilopoda have 

 the same three anterior pairs of legs, early and permanently devel- 

 oped as organs of manducation, while all other segments have but a 

 single pair. Palseontological evidence is in favor of the view that the 

 dorsal scutes of Diplopoda are compound. 



The SHjlit of insects. — The power of vision of insects has been investi- 

 gated by Prof. Felix Plateau, whose special aim was to determine 

 whether insects can distinguish the form of objects. It has been con- 

 tended by certain authors that such insects as possess compouud eyes 

 cannot distinguish form, and that vision operates in a different way 

 from that generally admitted, and consists mainly in the perception of 

 movements. To some extent this view is sustained by Professor Pla- 

 teau as the result of a series of experiments. He concluded from these 

 that '• insects only utilize their eyes to choose between a white luminous 

 orifice in a dark chamber, or another orifice or group of orifices equally 

 white. They are guided neither by odorous emanations, nor by differ- 

 ences of color. A fact which will certainly astonish all entomologists, 

 and likewise surprise the experimenter himself, is, that bees have as 

 bad sight and comport themselves almost as flies." 



Professor Plateau directed his observations to many widely different 

 insects, belonging to the orders of Diptera, Hymenoptera, Lepidotera, 

 Odonata, and Coleoptera, and the experiments spoken of were essen- 

 tially harmonious. The following conclusion resulted: 



(1) "Diurnal insects have need of a quick, strong light, and cannot 

 direct their movements in partial obscurity. 



(2) "In diurqal insects with compound eyes, the simple eyes offer so 

 little utility tliat it is right to consider them as rudimentary organs. 



(3) " Insects with compound eyes do not notice differences of form 

 existing between two light orifices, and are deceiv'ed by an excess of 

 luminous intensity as well as by the ai^parent excess of surface. In 

 short, they do not distinguish the form of objects, or, if they do, dis- 

 tinguish them very badly." {Am. Nat.^ v. 20, pp. 69, 70.) 



Adherence of insects to ceilings. — There has been considerable differ- 

 ence of opinion as to the method by which flies and insects generally 

 adhere to the ceilings and walls of rooms and analagous surfaces, and 

 the subject has recently been investigated by Herr H. DeWitz. His 

 researches tend to prove that the secretions by which flies, for example, 

 adhere to the window panes is not a thin fluid of a fatty nature, but 

 much more consistent. He adduces exi^eriments to controvert Eom- 

 bout's view that a fly can maintain itself on a glass surface by one leg 



