252 



HARDWICKE'S SCIENCE-GOSSIP. 



prey. The sight of such insects as these must range 

 over several feet at least, and within this field they 

 must be supposed to distinguish small objects with 

 rapidity and certainty. How can we suppose that an 

 eye without retinal screen, or accommodation for 

 distance, is coiripatihlc with sight so keen and dis- 

 criminating ? The answer is neither ready nor com- 

 plete, but our own eyesight shows how much may 

 be accomplished by means of instruments far from 

 optically perfect. According to Aubert, objects, to 

 be perceived as distinct by the human eye, must have 

 an angular distance of from 50" to 70", corresponding 

 to several retinal rods. Our vision is therefore 

 mosaic too, and the retinal rods which can be simul- 

 taneously affected comprise only a fraction of those 

 contained within the not very extensive area of the 

 effective retina. Still we are not conscious of any 

 break in the continuity of the field of vision. The 

 incessant and involuntary movements of the eyeball, 

 and the appreciable duration of the light-stimulus 

 partly explain the continuity of the image received 

 upon a discontinuous organ. Even more important 

 is the action of the judgment and imagination, which 

 complete the blanks in the sensorial picture, and 

 translate the shorthand of the retina into a full-length 

 description. That much of what we see is seen by 

 the mind only is attested by the inadequate impression 

 made upon us by a sudden glimpse of unfamiliar 

 objects. We need time and reflection to interpret 

 the hints flashed upon our eyes, and without time and 

 reflection we see nothing in its true relations. The 

 insect-eye may be far from optical perfection, and yet 

 as it ranges over known objects, the insect-mind, 

 trained to interpret colour, and varying brightness, 

 and parallax, may gain minute and accurate inform- 

 ation. Grant that the compound eye is imperfect and 

 even rude, if regarded as a camera ; this is not its 

 true character. It is intended to receive and inter- 

 pret flashing signals ; it is an optical telegraph. 



In closing this series of sketches we would say, that 

 what has been here set down comprises but a small 

 fraction of what has l:)een made out by many good 

 observers, while all that has been seen and studied 

 bears no ratio whatever to the inexhaustible detail 

 presented to us in the simplest insect. Whether in a 

 busy age it is worth while to dwell minutely upon the 

 structure and mode of life of so small a creature is a 

 ciuestion which we and our readers would probably 

 answer in a different sense from the majority of man- 

 kind. It seems to us that of all sulijects of study, 

 Life is the most deeply interesting to the living man, 

 and that to know some little of the possibilities of 

 life under various conditions is worth any expenditure 

 of pains and time. 



BIFURCATION OF THE ELM LEAF. 



AMONGST the many notices of the morphology 

 and teratology of plants and leaves which have 



Fig. 158. — Partial Divisions. 



Fig. 159. — Completed Division. 



Fig. 160. — Leaf of Ulimis 7nonta7ia, with trifid tip, but 110 

 I division of central vein. 



[I'.RRATfM. — Fig. 125, p. 207 should have been I 



placed with tlie arrow horizontal, and pointing to the j appeared in SciENCE-GossiP, I have not met with 



left. Fig. 121, p. 205 is magnified 15 times.] | any allusion to the peculiar tendency of the leaves o 



