HARDWICKE'S SCIENCE-GOSSIP. 



99 



The stroma consists of proteid substances, but as 

 development progresses the albuminous material 

 gives place to this highly refractive, probably oily 

 material, and then the lenticular portion of the 

 cornea becomes reticular after having been treated 

 with such'reagents as will dissolve out this interfibrillar 

 substance. About twelve years ago, when examining 

 the lateral portions of the compound eye of the 

 lobster, he continually found thickenings beneath the 

 rod-like bodies which united the corneal portion of 

 the eye with the nerve centres beneath, and he became 

 convinced that no nerve structure passed through this 

 membrane, and then it struck him that, in trying to 

 make out that this structure was retinal, he was doing 

 very much the same thing as examining the minute 

 structure of the crystalline lens of the vertebrata, and 

 coming to the conclusion that the rod-like fibres of 

 that lens were in themselves not merely a portion 

 of the refractive structure, but were actually the 

 terminals of the optic nerve. He regards the whole 

 of the structure developed from the superficial epi- 

 blast as a refracting organ, and with that view he had 

 termed it the dioptron, or the refractive portion of the 

 compound eye. In some insects which do not 

 undergo metamorphosis the great compound eye is at 

 first small, and consists only of a few facets, but a 

 new portion of the eye is developed at each shedding 

 of the integument. The nerve also gradually passes 

 to the surface, encircles the old nerve, and forms a 

 new retina. This goes on until at the last the optic 

 nerve is found very much spread out. During the 

 last shedding of the skin the whole of the retina 

 undergoes degeneration, and a new one] [takes its 

 place ; so that new sets of facets are developed at 

 each skin shedding, and a new retina is developed 

 from the nerve centres beneath the dioptron. 



In expounding the various theories of insect vision, 

 the lecturer explained that Midler's theory of 

 " mosaic vision " was not in itself tenable, because, 

 in the first place, the images produced would be 

 blurred, and surfaces of eight or ten inches square, 

 would only be visible as points at very moderate 

 distances — say, ten or twenty feet. The theory 

 which the lecturer propounded was that an inverted 

 sub-corneal image was formed beneath each corneal 

 facet, and the great rods of the dioptron produced a 

 magnified erect image of that portion of the sub- 

 corneal image which lies in the axis of each. The 

 integration of these images produces the retinal image 

 upon what he had described as the "neuron." This 

 image had actually been demonstrated by Sigismund 

 Exner of Vienna, who first showed it at the Cologne 

 Congress of Naturalists. The "mosaic view," or 

 MiiUer's theory announced about 1826, assumed that 

 the tubes of the dioptron only permitted axial light to 

 pass through them ; so that each tube of the dioptron 

 produces one distinct stimulation of the nerve, and 

 there could only be as many separate sensations of 

 light as there are tubes to the dioptron, a supposition 



which is quite incapable of explaining vision in an 

 insect which has perhaps only fifteen or twenty 

 lenticles of the eye, some only having five or six, 

 although others have as many as 24,000 to 30,000. 

 Even in those which have the largest number, the 

 acuity of vision is not sufficiently explained by 

 Midler's theory. 



OUR LANE. 



[Continued /rotn J>. 88.] 



THE upper reaches of our lane are much fre- 

 quented by that lovely and docile bird the 

 goldfinch {Cardiielis elcgans), for here the thistle- 

 heads afford him many a dainty meal ; his head- 

 quarters are, however, in my garden hedge, where, 

 secure from harm, he builds, and delights us with 

 his soft and cheerful strain. As sweet, though 

 less varied, is the song of the beautiful plumaged 

 chaffinch [Fringilla ccekbs), he, too, is a frequenter 

 of our lane, and throughout the early spring and 

 summer months pours out the gladness of his little 

 heart from daybreak till night casts her dark mantle 

 on all around. Nor must I forget my sober-coated 

 protege — most innocent of all the feathered tribe — 

 the hedge-warbler [Accentor 7nodularis). Use him 

 very gently, dear reader, he is a most lovable 

 bird ; soft and low, his plaintive song correctly in- 

 dicates his innocent nature. Drop for him the tiny 

 crumb. I love his presence, and glad am I to think 

 he is influenced by no migratory impulse. Need 

 it be said that that harmless bird whose trustful 

 nature leads him to seek man's companionship — his 

 little, bright- eyed friend, sweet robin red-breast 

 {Erythaca rubecida) attends us in our garden-strolls, 

 and claims his daily share of crumbs ; carolling his 

 bright song by way of thanks. To him, as it is to 

 others, our garden is a sanctuary, and well he seems 

 to love it. The yellow-ammer [Emberiza citrinelld)^ 

 too, he loves the hedges and pastures of our lane ; 

 but he, too, in our garden hedges and ivy builds, nor 

 do his oft-repeated notes pall on my ear. His 

 favourite perch is the vane of a weather-cock upon 

 the top of my summer-house, from whence, hour 

 after hour, he trills his little varied song ; this, too, 

 when the songs of other birds have long been hushed. 

 I always welcome the advent of that tiny bird the 

 chiff-chaff {Sylvia hippolais), together with that of the 

 whitethroat {Ctirnica cifterea). Not much have they 

 to boast of in the way of song, but their sweet 

 accompaniment to the richer melodies of other 

 feathered choristers make up the sum of a glorious 

 concert ; whilst high above the much-besoiled earth, 

 the skylark {Alauda arvensis) and the woodlark (A. 

 arborea) pour out at "Heaven's gate" their joyous 

 hymns of praise. 



Adjoining my garden is an arable field, and beyond, 

 and yet beyond are others, and here the former loves 



F 2 



