540 



THE SENSES AND SENSOR Y ORGANS. 



ommatea ; but when the final ecdysis occurs, a new optic 

 nerve and retina is developed, which replaces all the partial 

 nerves and retinas of the larval form (Fig. 70). This is formed 

 within the hemisphere, and grows outwards until it reaches 

 the inner surface of the dioptron ; the partial retime undergo 

 histolytic degeneration during its development. I think it 



I-'n;. 70. The development of the retina in the compound eye of a Dragon-fly 

 (Agrion] and of the Cockroach (Periplaneta). .-I, a section of the eye and optic 

 nerves of the larva of agrion from a specimen 12 mm. long ; />'. a similar section 

 from a more advanced larva ; C, a similar section from the nymph of the same ; 

 2), a section through the optic ganglion and nerve of a young Cockroach larva ; 

 </, the dioptron ; ..y 1 , the ganglion from which the larval optic nerves arise ; .;-', 

 the optic ganglion of the imago in a more or less rudimentary condition ; m l>, 

 the mcinl>rana liasilaris ; ;/', the retina of the larva consisting of separate 

 rctinul.u ; ;/-', the retina of the imago in a more or less rudimentary condition ; 

 /;, tracheal vessel. Reproduced from my paper [233] in the Trans, of the Linn. 

 Soc. 



< 'xcr-edingly probable that the remarkable 'kidney-shaped' 

 bodies described by Newton [213], in the optic ganglia of the 

 lobstrr, ;ire retinas and optic nerves, which replace the old 

 retime in successive ecdyses. 



Even in the Metabola there are traces of the development 



