THE DEVELOPMENT OF ADMETUS PUMILIO. 621 



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 retinee of the two eyes 

 are very distinctly separated from each other by a light nn- 

 pigmented line (s.). 



The post-retinal layer {pr.) resembles the epidermis else- 

 where. 



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 cephalo- 

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

 eyes. The latei-al eyes originate out of simple ectoderm 

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

 draAving (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 con- 

 sists of the following parts : — mouth, pharynx, oesophagus, 

 muscle-stomacli, 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 an I-shaped cavity, 

 the Avails of which are lined with a thin chitinous membrane. 

 Tlie cavity measures '1 mm. by '01 mm. 



The cells forming tlie walls of the pharynx have very dis- 

 tinct cell-walls ; the nuclei are small, oblong, and stain very 

 deeply with ha3matoxylin; they measure '007 mm. by "004 

 mm. Besides the lateral and dorsal muscles attached to this 

 part of the alimentary canal, described by Laurie, I must 

 draw attention to another set of muscles connected with the 

 pharynx. This set is a ring-muscle, which runs round the 

 pharynx ; it evidently acts as the antagonist of the lateral and 

 dorsal muscles, and serves to close the cavity when it has 

 been distracted by the other muscles. 



VOL. 45, FART 4. — NEW SERIES. T T 



