THE DEVELOPMENT OF THE COMPOUND EYE. 539 



Insecta, a fact which must be very well known, although I 

 have been unable to find an explicit statement that such is the 

 case. 



In some young Cockroaches (Periplaneta orientalis), less 

 than i centimetre long, I found the compound eye has about 

 200 ommatea, in which the pigment is developed, surrounded 

 by two or three rings of non-pigmented ommatea. In the 

 half-grown insect I estimated that the number has increased 

 to about 4,000, with a narrow ring of non-pigmented ommatea ; 

 whilst the full-grown Cockroach has about 8,000 ommatea, all 

 pigmented, in each eye. 



In the Metabola, in which the compound eyes are not de- 

 veloped until the final ecdysis, there is no such peripheral 

 growth of the eye ; but I observed long ago that the peripheral 

 ommatea are much less perfectly developed than the central 

 ommatea in all the earlier stages of development, and in the 

 Flies they frequently remain rudimentary throughout the whole 

 life of the insect. 



In the Cockroach, as I observed formerly [233], there is a 

 great difference between the changes which occur in the dif- 

 ferent ecdyses. Usually new nerves bud out from the hemi- 

 spheres with each addition to the number of ommatea, so that 

 in the young Cockroach the compound eye is innervated by 

 bundles of thick nerves, each supplying a small group of 



Bibliography : 



253. BOBRETZKI, N., Ke Embriologhil Chlemstonoghlkh ('On the Em- 

 bryology of Arthropods '). Zapiskl Kiev. Obshchest. Estestvois., iii. 

 (part 2). 1873, pp. 129-263 : 6 pis. 



254. BOBRETZKI, N. V., Ke voprosu o prolskhozhdenil blastodermuf u 

 nasyekomuikh ('On the Origin of the Blastoderm of Insects'). 

 Zapiski Kiev. Obshchest. Estestvois., v., 1877, PP- 2 39- 2 56- 



255. REICHKNBACH, H., 'Studien zur Entwicklungsgeschichte des Fluss- 

 krebses. Abh. Senckenberg. Naturf. Gess., Bd. xiv., 1886. 



256. KlNGSLEY, I. S., 'The Development of the Compound Eye of 

 Crangon.' Journ. of Morphology, vol. i., 1887. 



257. BERNARD, H. M., ' The Apodidas ; a Morphological Study.' Nature 

 series, 8vo, London and New York. 1892. 



258. JOHANSEN, H., 'Die Entvvicklung des Imagoauges von Vanessa 



urticae.' Zoologische Jahrbticher (Spengel), Band vi., Abth. Anat., 

 1893. 



