50 KINGSLEY. [Vol. I. 



In the figures which illustrate this article no artistic or dia- 

 grammatic latitude has been allowed, except where expressly- 

 stated, each nucleus being drawn by the Oberhauser camera. 

 While in surface-views of the early stages the cell-boundaries 

 seem very distinct, they are but very rarely visible in the sec- 

 tions of embryonic stages (possibly the result of Perenyi's fluid), 

 and hence the following account deals almost wholly with nuclei 

 rather than with cells. 



Development. 



The first appearance of the compound eyes is shown in Fig. i, 

 which represents the egg of Crangon very soon after the closure 

 of the blastopore. In the median line is shown the, as yet, un- 

 differentiated germinal area of the body while at ol, on either 

 side, are the optic lobes, or better, optic discs. , These three 

 regions indicated are readily recognized by the character of the 

 cells. These in superficial area are smaller than those of the 

 rest of the blastoderm ; but in section they are much deeper. 

 Each optic lobe is connected with the central area by a row of 

 but slightly larger cells, the ultimate fate of which is to enter 

 into the composition of the brain, though all parts of this organ 

 are not derived from them. As seen in a side view, the optic 

 lobes are oval, the major axis being about one and one-third 

 the length of the minor. The distance between the optic lobes 

 differs somewhat in different eggs, being usually a little less 

 than in the specimen figured. This may, however, be a result 

 of development, for not all the eggs taken from the same shrimp 

 seem to be of exactly the same age. A transverse section of 

 one of the optic lobes at an early stage is shown in Fig. 2. The 

 cell-boundaries are not visible, but the arrangement of the oval 

 nuclei clearly indicates that here the epiblast is to be regarded 

 as but a single cell in thickness. Immediately beneath the 

 slightly stained protoplasm comes the yolk. Near the centre 

 of the lobe is seen the first stage of the optic invagination. 

 Seven of the nuclei are sunk below the rest, and form in outline 

 a shallow cup {pi), the concavity of which is directed outward. 

 The larger nucleus at one side is about to divide, although no 

 karyokinetic figures are visible. 



This pit rapidly grows deeper, and, extending outwards, 

 downwards, and forw^ards, soon comes to occupy a position 



