- 26 — 



6. The Eyes. — The median eyes have become 

 much further developed since the fourth stage. This can 

 best be described in connection with the drawing (fig. 6). 

 The median eyes are still situated on a fold in front of 

 the mouth. The mouth opens into the cavity (c.) formed 

 between the fold carrying the eyes and the cephalothorax. 

 We can distinguish between three distinct layers of the 

 fold — the corneal, the retinal, and the sub -retinal layer. 

 This last is separated from the retinal by a fissure. 



The stratum corneum (co.) consists of a layer of nuclei, 

 two or three deep. In front it has begun to deposit chitin, 

 the future lens (I,) 



Under the cornea lies the retina (r.) It is deeply 

 pigmented in its anterior half. One can distinguish thicker 

 and thinner lines of pigment (p.) in front. The retinae of 

 the two eyes are very distinctly separated from each other 

 by a light unpigmented line (s.). 



The post-retinal layer (pr.) resembles the epidermis 

 elsewhere. 



I am not in a position to say how the eye has 

 developed out of the Anlage described in the fourth 

 stage. 



There are three lateral eyes on each side of the cepha- 

 lothorax. They lie in groups in a line with the median 

 eyes. The lateral eyes originate out of simple ectoderm 

 thickenings, as Laurie stated, as will be seen in the 

 drawing (fig. 7). Pigment is as yet only deposited in the 

 spaces between the single eyes. The lateral eyes of the 

 adult also consist of three facets. 



7. The Alimentary Canal. — Since the fourth 

 stage the alimentary canal has made very rapid progress. 

 It now forms a nearly complete tube, only the foremost 

 part of the midgut remaining absent. The alimentary canal 

 now consists of the following parts: — mouth, pharynx, 

 oesophagus, muscle-stomach, midgut, and rectum. The 

 mouth is situated on a small protuberance, which projects 

 into the subocular cavity, and lies between the bases of 

 the pedipalpi. Just behind the mouth we find the pharynx; 

 that has a I- shaped cavity, the walls of which are lined 



