xlv 



acute vision of very near objects. It is chiefly developed in 

 predaceous insects. It probably serves the insect in judging of 

 the distance of objects from the mouth." 



Mr. Lowne describes specially the eyes of Spjihns, Musca, 

 Eristalis, Tipula, Vesim, Formica, Agrion, Acridium, Vanessa, 

 Sphinx, and Noctua. He finds the eye of Sphinx to be inter- 

 mediate between those of the nocturnal and diurnal Lepidoptera, 

 while the highest development of the "aggregate eye" occurs in 

 the so-called compound eyes of the Nematocerous Diptera and 

 the Hymenoptera. He considers the eye of the Daddy Long-legs 

 {Tipula) to be intermediate in structure between a true compound 

 eye and a collection of ocelli — a view, however, which seems to 

 present considerable difficulties. As regards the power of vision 

 possessed by the compound eyes, he believes that a dragon-fly or 

 a wasp sees an object at a distance of twenty feet "in the same 

 detail that a man would perceive it if it were seen at a distance 

 of one hundred and sixty feet." On this point some observations 

 of M. Fabre's are of much interest. Some years ago I tried 

 myself the experiment of taking bees to some distance from 

 home, and then letting them go. They rose in the air, just as a 

 pigeon does under similar circumstances, and ere long returned 

 home. I was, however, prevented from following up these 

 observations. M. Fabre has now made similar experiments, and 

 finds that if bees are taken as far as four kilometres from home, 

 they will still find their way back. It would be very interesting 

 to make these experiments for greater distances, but the facts 

 already ascertained surely indicate considerable powers of 

 vision. 



As regards the structure of ocelli, Graber* differs materially 

 from Grenacher. He observes that, according to the latter, the 

 whole complex structure from the termination of the optic nerve 

 to the hinder surface of the cornea forms one cell. Graber, on the 

 other hand, considers that it is composed of two. He observes 

 that Grenacher considers the nucleus of his single cell to be 

 sometimes pre-bacillar, sometimes post-bacillar. These, however, 

 Graber regards as really the nuclei of two different series of cells. 

 He considers that the ocellus of the scorpion offers in some 

 respects an interesting intermediate form between the simple 

 and compound eye. In fact, his account of their delicate and 

 * Ar. f. Mic. Anat., 1880, xvii., p. 58. 



