52 KINGSLEY. [Vol. I. 



attention. The nuclei of both gangliogen and retinogen have 

 become elongated at right angles to the surfaces of the layers, 

 and several nucleoli are visible in each. The subsequent stages 

 increase this peculiarity until the nuclei attain a length of three 

 or four times their shorter axis. In this process those of the 

 gangliogen are in advance of those of the other layer, and in 

 them division takes place first. Then the retinogen follows 

 through almost exactly the same phases, which can be under- 

 stood by a reference to Fig. 6, which represents the eye in an 

 embryo, in which seven pairs of appendages have become out- 

 lined. Here the nuclei of the retinogen are elongate, but 

 those of the gangliogen have divided transversely, each giving 

 rise to a series of nuclei arranged in a single row, and directed 

 towards the centre of the &%'g. This structure does not show so 

 plainly in the figure as it would were the figure more diagram- 

 matic, but it is readily recognizable on one side of the drawing, 

 which is an exact copy of the section. It is next to impossible 

 to cut the sections so exactly as to pass precisely in the desired 

 plane, but a study of the consecutive sections clearly shows this 

 radial arrangement, and also that all the nuclei in each row 

 arise from the corresponding nucleus of the gangliogen, and 

 extend inwards. This process of division continues until each 

 ganglionic row consists of six nuclei before any other change in 

 this region occurs. When these ganglionic rows are formed 

 the nuclei of the retinogen have reached their greatest length, 

 but have not yet begun to divide transversely, nor is there as yet 

 any indication of an arrangement into groups. The general 

 appearance, as shown in sections, can be seen from Fig. 6. The 

 pyriform shape of some of the nuclei is due to their being cut 

 obliquely ; it is further noticeable that the more dorsal nuclei 

 are more elongate than those nearer the ventral surface. The 

 ectoderm is a thin layer with scattered nuclei. 



At this stage still another element begins to enter the eye. 

 Fig. 12 is a section from the same embryo as that shown in Fig. 

 6, but is taken a short distance further back. Here all the 

 features described above are clearly seen, but in addition there 

 are some others. In the lower centre is the cephalic ganglion 

 with the fibrous portions already developed. Immediately 

 above this is shown a thin layer of tissue with elongate or fusi- 

 form nuclei, easily distinguishable from all the rest. This is the 



