THE EMBRYOLOGY OP A SOOEPION. 131 



the same size as those of the median ones. The pigment is not^ 

 however, arranged in definite zones, though it is more abundant 

 at the base and at the outer ends of the cells than in the middle. 

 There is a small third lateral eye present, and the hypodermis 

 around and — the lateral eyes being so to to say on the edge of 

 the head — below the eyes is all pigmented. I have been 

 unable to find the nerve to these eyes and think it is probably 

 not yet formed. The cuticle over the lateral eyes is not 

 thickened to form the lens, and I have seen no sign of the 

 peculiar mode of lens-formation described by Parker,^ i. e. the 

 ends of the perineural cells pushing in front of the retina. It 

 is, of course, possible that this does not take place till later. 



The brain and ventral cord have almost attained their 

 adult structure. In the nerve- cord there is a string of 

 cells in the middle line (PL XVIII, fig. 60) dorsal to the 

 cords proper, which seems to represent the centre of the neural 

 groove. 



The tail is exactly similar to that of the adult, and is carried 

 in the same way curved over the back. The poison-glands are 

 fully formed and surrounded by muscles, but do not occupy so 

 much of the terminal segment as in the adult. The proctodaeum 

 is lined by flat cells and has pushed its way almost to the 

 base of the tail. The mesenteron is fully formed only in the 

 hind segments of the body (PI. XVIII, fig. 60). From the 

 end of the stomodaeum to where the last hepatic cseca 

 join it the intestine (fig. 61) is surrounded by a definite 

 cylindrical layer of mesoblast which is continuous with that 

 surrounding the lobes of the liver, but the hypoblast cells 

 lining this cylinder (fig. 61, hy.) are not yet definitely arranged. 

 The nuclei are scattered about in groups for the most part 

 near the outside, and the cells are drawn out into irregular 

 more or less pyramidal form, the apex of the pyramid pointing 

 towards the centre of the tube. There is no definite lumen, 

 the space between the cells being filled up by small yolk-spheres 



(fig. 61, 7/A'.). 



The liver-follicles are much the same in structure as the 

 1 Loc. cit., p. 199. 



