262 



Mr. B. T. Lowne on the Modifications of [Mar. 28, 



number of recipient rods shew that it is most probable that the func- 

 tion of the ocelli is rather the perception of the intensity and the 

 direction of light than of the actual disposition and colours of sur- 

 rounding objects. 



The compound eyes of insects are of two kinds ; an intermediate 

 condition between the simple and compound eye, closely resembling the 

 aggregate eyes of other anthropods, which I have at present only found 

 in the ISTematocerous Diptera, and in the bees, wasps, and ants, the 

 only examples of the Hymenoptera in which I have examined the eyes ; 

 and the true compound eye, found in the majority of insects. 



I strongly suspect that further observations will show that the aggre- 

 gate form of eye is also characteristic of the Hemiptera and of a large 

 number of the Coleoptera ; I hold this view, from a casual observa- 

 tion of the eyes of several species of Hemiptera, as well as from the 

 imperfect description of the eyes of these insects in Dr. Grenacher's 

 recent paper. 



I have examined and described the eyes of Tipula, Formica, and 

 Vespa, which are examples of very highly modified aggregate eyes. In 

 these insects each facet of the cornea has sixteen recipient rod cells 

 behind it. In Tipula these are so deeply pigmented, that in the adult 

 insect it is impossible to get a transparent section ; although I have 

 adopted the method described by Dr. Schaefer in the preparation of 

 fine sections of the mammalian ovum,* of imbedding the specimen in 

 cacao butter, and have cut sections of certainly not more than T ^ of 

 an inch in thickness. These have been examined with a sixteenth 

 immersion of JSTachet's. 



The nearest approach to these deeply pigmented cells is seen in the 

 red cones in the eye of the pigeon, described by Max Schultze,f or 

 perhaps in the deeply coloured rods of the eel (Kuhne).J But, unlike 

 the latter, the pigmented parts of the eyes of insects, as far as my 

 observations go, are unaffected by light, and the same observation has 

 been made by Kuhne with regard to the colour in the so-called rods in 

 the eye of the lobster. § 



Behind the corneal facet, and immediately in relation with it, each 

 rod-cell has a minute highly refractive spherule ; this is of an intense 

 purple colour in the eye of Vespa and Tipula, but it is colourless in the 

 eye of Formica rufa. It is exceedingly like the globule found between 

 the inner and outer segments of the cones in many birds. 



Behind the rod-cells a very remarkable structure is found which has 

 hitherto escaped detection, except by Dr. Grrenacher,|| who describes it 

 under the name retinula. As this term is, however, applied by him to 



# " Proc. Roy. Soc." f " Archiy," Bd. iii. 



X Kiilme " Untersuch. aus dera Physiolog. Inst, der Uniy. Heidelberg," Bd. i, 

 Hft, i. § Ibid, hft. ii. 



|| " Zehender's Monatsblatt. Beigeheft," 1877. 



