202 patten: [Vol. I. 



enings which I shall call nerve-spindles ; the part of the retinal 

 ganglion in which they are formed, I have called the nerve-spindle 

 layer. Surrounding the nerve-spindles are unipolar ganglion- 

 cells which appear to be attached to the spindles by very short 

 fibres. In the outer layer of the retinal ganglion the spindles 

 are reduced to fibres, to which are attached clusters of unipolar 

 CTanCTJion-cells. These clusters of cells attached to the main 



o o 



fibre are similar to the much longer ganglion cell-stalks forming 

 the cortical layer of the optic ganglion. 



After passing that part of the brain-sheath lying against the 

 distal surface of the retinal ganglion the main fibres unite in 

 large bundles to form the nerve-bundle layer. 



Beneath the nerve-spindle layer is what appears to be a dis- 

 tinct membrane, but careful examination shows that it is a layer 

 of nerve-fibres running at right angles to the spindles. There 

 are also a few scattered ganglion-cells beneath the nerve- 

 spindle layer. 



The nerve-bundle layer contains, in the pupal stage, large, 

 round cells filled with deeply-stained yolk-like globules (Fig. 

 Tjt.c). 



During the pupal stage the optic invagination closes. The 

 actual closure I have not observed. At the latest period seen 

 before the closure the anterior and posterior folds covered more 

 than half of the eye. On the edges of the eye the cells composing 

 the two limbs of the folds had already assumed the shape and 

 arrangement characteristic of the outer and middle layer of the 

 eye in the next stage. In the earliest pupal stage after the 

 closure the folds had disappeared, wJiile above the ommatenm 

 was a double layer of cells exactly like those seen on the pe- 

 riphery of the eye in the preceding stage. It is therefore evi- 

 dent that these two layers are derived from the coalesced limbs 

 of the dorsal and ventral folds. 



At the beginning of the pupal stage, then, the eye consists 

 of three layers, the inner one being the ommateum, which is in 

 practically the same condition that it was before the closing of 

 the flattened invagination ; the middle layer is composed of 

 cells containing large, round nuclei arranged at regular intervals 

 over the retinophorse ; the third layer is composed of flattened 

 cells with quite small nuclei ; it is retained with very slight modi- 

 fications as the corneagen of the adult. The cells of the middle 



