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 1 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 [288], 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 
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nasyekomuikh (‘On the Origin of the Blastoderm of Insects’), 
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255. REICHENBACH, H., ‘Studien zur Entwicklungsgeschichte des Fluss- 
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