Entomology : with special reference to its biological and economic aspects . only objectsat a definite distance could be imaged. The limit of the perception of formby insects is placed at about two metersfor Lanipyris, meters for Lepi-doptera, 68 cm. for Diptera and 58 Hymenoptera. It is generally agreed, however, thatthe compound eyes are specially adaptedto perceive movements of objects. Thesensitiveness of insects to even slightmovements is a matter of common ob-servation ; often, however, these insects can be picked up withthe fingers, if the operation is performed slowly until
Entomology : with special reference to its biological and economic aspects . only objectsat a definite distance could be imaged. The limit of the perception of formby insects is placed at about two metersfor Lanipyris, meters for Lepi-doptera, 68 cm. for Diptera and 58 Hymenoptera. It is generally agreed, however, thatthe compound eyes are specially adaptedto perceive movements of objects. Thesensitiveness of insects to even slightmovements is a matter of common ob-servation ; often, however, these insects can be picked up withthe fingers, if the operation is performed slowly until the insectis within the grasp. A moving object affects different facets insuccession, without necessitating any turning of the eyes or thehead, as in vertebrates. Furthermore, on the same principle,the compound eyes are serviceable for the perception of formwhen the insect itself is moving rapidly. The arrangement of the pigment depends adaptively uponthe c[uality of the light, as Stefanowska and Exner haveshown; thus, when the light is too strong, the iris and retinal9. Diagram of otiter, trans-parent portion of an omma-tidium to illustrate thetransmission of an axial ray(^A) and the repeated reflec-tion and absorption of anoblique ray (B), which atlength emerges at C. p, irispigment. I 14 ENTOMOLOGY pigment cells elongate around the ommatidium and their pig-ment granules absorb from the cone cells and rhabdom theexcess of light. If the light is weak, they shorten, and absorbbut a minimum amount of light. Origin of Compound Eye.—The compound eye is oftensaid to represent a group of ocelli, chiefly for the reason thatexternally there appears to be a transition from simple eyes,through agglomerate eyes, to the facetted type. This plausi-ble view, however, is probably incorrect, for these reasonsamong others. In the ocellus, a single lens serves for allthe retinul?e, while in the compound eye there are as manylenses as there are retinulse. Moreover, ocelli do not passdirectly
Size: 1143px × 2186px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
