Miscellaneous. 79 



course of the metamorphosis, and give us some authentic informa- 

 tion as to the morphological significance of the pedunculated e3'es. 

 In a previous memoir* I have already discussed them, and have 

 shown that the movable pedunculated eyes represent the abstricted 

 lateral parts of the head which have become independent. It 

 occurred to me to trace the process of development more in detail, 

 and in this way to ascertain the relations of the so-called eye- 

 ganglion, on the one hand to the cerebrum, and on the other to the 

 retina-ganglion, as also to the elements of the eye itself, and also 

 to work out the hitherto imperfectly-known minute structure of the 

 latter. 



The foundation of the lateral eye is perceptible even in meta- 

 nauplius-larvte, the tissues of which have become clear, as a broad, 

 pad-Kke, hypodermal thickening placed laterally to the frontal 

 organ. The cell-growth is continued inwards, and here contains 

 the material for the eje-ganglion, which is united with the brain. 

 Tlie pigment first appears in the lateral parts of the eyes, in whicli, 

 at the same time, the first crystalline cones show themselves as small 

 refringent bodies. The derivatives of the hypodermal cells are 

 there already divided into a suj)erficial layer for the formation of 

 the crystalline cones, and a deeper layer for the nervous rods and 

 pigment, which is continuously connected by trains of fibre-bundles 

 with the cell-mass, which is in course of conversion into the retina- 

 and eye-ganglia. The latter has been produced simultaneously 

 with the foundation of the eye, as a deep-seated layer of the hypo- 

 dermal swelling, which has been previously indicated by me as the 

 matrix of the eye. This, however, not only effects the greatly in- 

 creasing extension (with advancing growth) of the eye-segment, 

 which afterwards separates as the pedunculate eye, but at the same 

 time furnishes the material for the increase of the elements of the eye 

 and the retina, as also of the eye-ganglion. The sagittal zone-like 

 hypodermal cushion consequently, to some extent, represents the 

 gemmation-zone both of the eye and of the nerve-mass occurring 

 within the eye-peduncle, the laterally produced cells furnishing the 

 crystalline cones and nervous rods, while the elements which advance 

 inwardly and mesially strengthen the eye-ganglion. 



In this nerve-mass in the interior of the eye-peduncle, distin- 

 guished as the eye-ganglion, we distinguish two portions, both of 

 which proceed, by continuous growth, from the band-like gemmation- 

 zone, namely, a distal retinal part turned towards the base of the 

 hemisphere of the eye, and a proximal segment united with the 

 cerebrum, the eye-ganglion sensu stnctiori. 



The latter contains a central mass of parenchyma and a super- 

 ficial coat of ganglion-cells, which appears to be considerably thick- 

 ened on the anterior surface, and gradually disappears towards the 

 posterior concavely incurvate side. 



The fibre-trains of the parenchymatous layer, radiating from the 

 cerebriim, traverse the eye-ganglion transversely in a straight course, 



* ' Zur Kenntniss des Baues uud der Entwickelung von Apus cancrifor- 

 mis und Branchipus stagnalis ' (Gottingen, 1873). 



