Archive image from page 172 of The anatomy, physiology, morphology and. The anatomy, physiology, morphology and development of the blow-fly (Calliphora erythrocephala.) A study in the comparative anatomy and morphology of insects; with plates and illustrations executed directly from the drawings of the author; CUbiodiversity4765349-9875 Year: 1890 ( THE DEVELOPMENT OF THE NERVOUS SYSTEM. 485 'The ganglio-genetic cells, which at first are few in number, increase and multiply, without, however, changing their char- acter, and always remaining disposed in a single layer. ' In the seventh stage t
Archive image from page 172 of The anatomy, physiology, morphology and. The anatomy, physiology, morphology and development of the blow-fly (Calliphora erythrocephala.) A study in the comparative anatomy and morphology of insects; with plates and illustrations executed directly from the drawings of the author; CUbiodiversity4765349-9875 Year: 1890 ( THE DEVELOPMENT OF THE NERVOUS SYSTEM. 485 'The ganglio-genetic cells, which at first are few in number, increase and multiply, without, however, changing their char- acter, and always remaining disposed in a single layer. ' In the seventh stage these cells cease to produce elements similar to themselves, and give rise on their deep surface to much smaller elements very poor in protoplasm, with nuclei easily stained by carmine which may be designated as ganglion cells; as soon as these are formed they themselves multiply very actively. Owing to this multiplication, the first proto- cerebral lobe becomes a mass of cells convex externally and concave within. ' It consists, then, of two layers of cells which are very distinct, a superficial layer on its convex surface of ganglio- FlG. 63. A sagittal section through the outer part of the hemisphere of the adult larva showing the invagination of the mantle layer from which the retina of the imago is developed, d, invaginated layer surrounding the retinal rudiment ; e', epithelial mantle layer; /, part of the pyramidal ganglion ; /, superficial cells of the optic ganglion ; 0, central stroma of optic ganglion ; /, group of small cells invaginated in the cavity of the rudimentary retina. genetic cells and a deeper portion consisting of numerous layers of ganglion cells.' So far Viallanes' description appears to be extremely clear, and to correspond closely with the phenomena observed in the Blow-fly by myself. It is possible that the deeper layers of cells are formed from the mantle layer. In two regions I have seen appearances which seem to
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