228 



SCIENCE-GOSSIP. 



[Oct. 1, 1865. 



ON THE COMPOUND EYES OE INSECTS. 



IN Mr. Lewis G. Mills's very interesting paper 

 on llie spiracles of the fly, in Science Gossip 

 for September, be remarks— " The head of the fly 

 contains the compound eyes with which it sees." 

 This sentence revived a thouglit tliat 1 have often had 

 before, and for wliich I am indebted to Mr. Walker for 

 bringing into existence ; namely— Is this wonderful 

 compound structure an organ of sight ? I presume 

 that all readers of Science Gossip are familiar with 

 the polygonal facets, and tlie fine hairs springing 

 from between, which form the so-called compound 

 eyes of insects ; and I think all who have given the 

 subject any attention will allow that these organs 

 seem singularly uuadapted for vision. An excellent 

 idea of the incompatibility of an organ so con- 

 structed for the purpose of sight may be obtained 

 by looking in a subdivided convex mirror, in which 

 it will be seen that objects reflected are broken into 

 confused distorted masses. Cuvier, speaking on 

 this subject, says that the structure is so very dif- 

 ferent from that of other animals, that it would be 

 difficult to believe it an organ of sight, had not 

 experiments demonstrated its use. The experi- 

 ments referred to were covering the compound eyes 

 of a dragon-fly, which was then found to dash against 

 objects in its flight, with every appearance of blind- 

 ness. A wasp was treated in the same manner, and 

 it ascended perpendicularly in the air, until it com- 

 pletely disappeared. Upon the simple eyes being 

 covered also, it did not attempt to fly, but remained 

 immovable. " How futile these arguments are," 

 says Walker, in his admirable work upon the 

 nervous system, " need scarcely be pointed out. 

 The same results would occur if these were organs 

 of touch, equally essential to the guidance of in- 

 sects." Another fact pointed out by Walker tends 

 to overthrow the theory of tliese compound struc- 

 tures being organs of vision, which is, that the 

 black coat {pigmentum nignini) is external to what 

 may be termed the retina. The Gossiper in science 

 will the better understand this by the following 

 simple experiment :— Let him open the window of 

 his room and hold the crown of his hat (if a black 

 one) parallel to the glass on the outside ; he will 

 then find that, looking at the crown of his hat 

 through the pane, his face will be reflected. This 

 is a simple illustration of the action of the human 

 eye. The hat represents the dark pigment, the 

 glass the retina, and the man the object looked at. 

 Now, in the so-called compound eyes of insects, the 

 dark pigment is before, instead of behind the retina, 

 and hence, as Walker observes, " comparative ana- 

 tomists complain lamentably of the difliculty of 

 understanding how, under such circumstances, 

 vision can take place." Erom these and other cir- 

 cumstances. Walker hardly admits of a doubt but 



that the so-called compound eyes of insects are 

 organs of touch. He says—" Is not, then, the white 

 matter, well supplied with nerves, in these eyes, 

 analogous to a portion of the true skin of the higher 

 animals ; the black matter, to the mucous net-work, 

 which is dark in the negro, whose sensibility is 

 greatest ; and the exterior substance to the cuticle, 

 in itself insensible even in man, and horny in insects, 

 because their general surface is more or less so, 

 but furnished with fine hairs, which in them are 

 separated and supported by the hexagonal facets, 

 and descend through the black substance to the 

 true skin and its nervous fibrils." The hairs arising 

 from between the facets may be compared to the 

 whiskers of the cat, the extreme sensibility of which 

 is well known. A very simple experiment, that I 

 have often tried, tends, I think, to prove that the 

 so-called compound eyes are organs of touch. Let 

 the reader stand by liis window until a fly settles on 

 the outside of the glass, and then let him move his 

 hand about over the inside, being careful not to 

 cause any vibration, and it will be found that the 

 fly will not be disturbed. The reason of this is 

 obvious, if we allow the compound eyes to be organs 

 of touch, the simple eyes being placed on the top of 

 the head (as in the bee),— the interior of the room 

 is hidden from the creature's sight, and the inter- 

 vening glass destroys the exquisite sense of touch, 

 that would otherwise give it warning of the approach 

 of our hand. 



If this should be the means of causing those 

 better adapted than myself to give their attention 

 to this interesting question, my end will be attained. 



H. Yokes. 



VARIATIONS IN BRITISH PLANTS. 



N an early number of Science Gossip I made a 

 few remarks upon the varieties of British plants 

 which had come under my notice. As the present 

 year has enabled me to make several additions to 

 my list, I may perhaps be allowed a short space in 

 which to record my observations, premising that 

 they have all been made in the neighbourhood of 

 High Wycombe, Bucks. 



The Wood Anemone {Anemone nemorosa) varies 

 greatly in the number of its sepals ; I have found 

 specimens with five, six, seven, and eight respec- 

 tively. Perhaps the most curious malformation 

 which I have noticed is one in the Corn Poppy 

 {Papaver lihoeas), which occurred in a corn-field 

 near West Wycombe. The specimen alluded to 

 had a persistent calyx, formed of four sepals, two 

 of which were opposite at the base of the petals, 

 and the other two at short distances down the 

 stalk; all were much larger than is usually the 

 case, and the upper two seemed part sepal and part 

 petal, as they were streaked with red, and in some 



