MUSEUM OF COMPARATIVE ZOOLOGY. 103 
PLATE II. 
Fig. 10. Median face of a sagittal section through the anterior median eye of the 
left side, several days after hatching. The bacilli have begun to appear, and the 
fibres of the optic nerve are seen to be distributed to the retinal cells near their 
nuclei, — between them and the forming bacilli. The flattened nuclei of the post- 
retinal tract still indicate the presence of a distinct layer of cells behind the retina. 
The distance between the place where the optic nerve emerges and the ‘“‘lentigen ”’ is 
greater than at first. (Compare Fig. 1.) 
Figs. 11, 12. Two successive sagittal sections of the anterior and post. median eyes 
of the left side (median face) and of the same age as the preceding. The tapetum 
of the posterior eyes is already formed. 
Fig. 11. The optic nerve of the post. eye communicates with the middle of the 
post-retinal layer. A large portion of the median half of the tapetum removed with 
this section. The optic-nerve fibres of the anterior eye (not drawn) were distributed, 
as in Fig. 10. 
Fig. 12. The general direction of the original infolding is still evident in the pos- 
terior eye. The post-retinal layer is continuous with the hypodermis in front of the 
eye, and the pre-retinal behind. The bacilli at the anterior edge of the eye are partly 
obscured by an overlying portion of the tapetum, in which are to be seen the elon- 
gated nuclei. Beneath the outline of the anterior eye the optic nerve of the anterior 
lateral eye of the same side is cut obliquely. 
PLATE III. 
Figs. 13-15. Lateral faces of three successive sagittal sections, through the lateral 
eyes of the right side. From the same spider as Figs. 11 and 12. 
Fig. 13. Beyond the plate-like bacilli (consult the text, pp. 82, 83) is the tapetum 
with its longitudinal, uneven fissure, flanked on either side by the nuclei of the reti- 
nal cells, which are scanty immediately in front of the tapetum. 
Fig. 14. Section through the bottom of the canoe-shaped tapetum of the post. eye, 
showing the fissure and some of the nuclei of the flanking retinal cells, as well as 
some of the narrower marginal nuclei of the post-retinal layer. In the anterior eye 
are to be seen the post-retinal layer and some of the cells of the retina. 
Fig. 15. Only the nuclei of the post-retinal layer indicate the posterior eye. The 
tapetum of the anterior eye is cut lengthwise near its middle. All four layers are 
distinguishable, the bacilli being already developed. 
Fig. 16. Lateral face of a sagittal section through the posterior and anterior median 
eyes (the latter in outline) from the left side of a specimen one day after hatching, 
showing the four tracts of the posterior eye before the appearance of tapetum or 
bacilli. 
Fig. 17. Theridium tepidariorum, C. K., adult. Portion of a sagittal section — 
lateral face — passing though the tapetum of the posterior lateral eye of the right side. 
The outer border of the tapetum is obscured by pigment-granules of the post-tapetal 
layer, extending outward to the oval outline. The tapetal plates are large and quite 
regularly arranged; the tapetal fissure is broad and irregular in outline. 
