102 BULLETIN OF THE 



that the four regions are not as distinctly shown as in Fig. 2. In the post-retinal 

 region (anterior margin of the eye) there is a single cell which differs from the ordi- 

 nary hypodermal cells and resembles the cells with spherical nuclei found through- 

 out the body-cavity. I am unable to say whether it is a hypodermal cell preparatory 

 to division, or an intrusive element of different origin. The region in front of this eye 

 embraces three successive layers, — nearest the median plane a portion of the lateral 

 ■wall of the anterior median eye; beyond this, a portion of the muscles above de- 

 scribed, distinguishable by the direction of their very large (seen flat-wise ?) nuclei; 

 and finally beyond the latter the median wall of the anterior lateral eye. The nuclei 

 of the latter are reproduced in 



Fig. 3a, to show more accurately the arrangement of the cells. The four smaller 

 nuclei near the middle of the group correspond in position with the faintly stained 

 nuclei of the tapetum in the following figure, and undoubtedly belong to the tapetal 

 layer. 



Fig. 4. This section embraces the middle portion of the anterior lateral eye, the 

 muscular bands which pass between the post, median and post, lateral eyes, and a por- 

 tion of the median wall of the latter (post-retinal tract). The nuclei of the tapetal 

 region are arranged as though resulting from an outfolding between retinal and post- 

 retinal layers. Most of the nuclei in the anterior layer of this fold are less deeply 

 stained than those of the posterior layer. In this and the three following figures the 

 position of the poison-glands is shown at gl. 



Fig. 5. The region of tangency between the lateral eyes and their mutual flatten- 

 ing is shown. The post-retinal tracts of both eyes are in contact. The tapetal cells 

 and the post-retinal tract of the anterior eye are separated by the space of the original 

 infolding. The distinction between the different tracts of the posterior eye is not 

 readily to be made out, since the section embraces a part of its median wall; but some 

 of the nuclei near the middle probably are tapetal. In the next section. 



Fig. 6, the posterior lateral eye is cut nearly through the middle. The axis of the 

 eye being nearly perpendicular to the plane of the section, the latter embraces in the 

 centre only retinal cells flanked by a few tipetal cells, the latter being separated by a 

 narrow interval from the post-tapetal tract. The lateral region of the anterior eye, 

 which appears in this section, is composed principally of pre-retinal cells. 



Fig. 7 shows the extreme lateral margin of the anterior (lateral) eye, and a section 

 of the posterior eye near its lateral margin. In the latter are to be seen in the centre 

 the nuclei of the retinal cells; to the left and beyond them, those of the pre-retinal 

 cells ; and to the right the post-retinal cells, separated from the retinal elements 

 by a clear space. 



Fig. 8. Lateral face of a sagittal section through the anterior and posterior median 

 eyes of the left side. The tapetal tract appears to be represented by a single row of 

 nuclei. Consult the text, pp. 75-83. 



Fig. 9. Median face of a sagittal section through the posterior median eye of the 

 right side. A single faintly-stained nucleus in front of the retinal nuclei apparently 

 belongs to a tapetal cell, and thus suggests the existence of a fold in the tapetal 

 layer. This opinion is strengthened by the prolongation of the other tapetal cells 

 towards the region of the supposed outfolding. The tapering ends of the tapetal 

 nuclei jroint to the same region, but the lines representing the cell-boundaries have 

 not been printed with sufficient distinctness. Consult the text, pp. 75-83. 



