58 AETHUR DENDY. 



there is very little pigment except for a broad transverse band, 

 incomplete in the middle, which runs inwards from in front of 

 each eye. Around the eyes are well-marked radiating bands of 

 pigment, and on the sides and under surface of the throat and 

 chin are seen irregular longitudinal bands of grey on a white 

 ground. Numerous very minute round white dots are scattered 

 over the upper surface of the head. 



In embryo No. 2 the total length measured along the curve 

 of the back from the tip of the snout to the tip of the tail was 

 about 55 mm., of which the tail occupied about 22 mm. 



The only internal structures which I propose to speak of at 

 this stage are the parietal eye and its immediate surroundings, 

 and as these will be fully dealt with in a special memoir they 

 need not detain us long here. 



By the approximation of the cerebral hemispheres and optic 

 lobes in the straightening out of the cranial flexure the roof of 

 the thalamencephalon has become thrown into folds, and at 

 the same time strongly arched uj)wards. 



At the commencement of this stage the parietal eye lies close 

 over the end of its so-called " stalk ^' and above the hinder part 

 of the roof of the thalamencephalon. In July embryos, how- 

 ever, it has shifted forwards till it is separated from the end of 

 its ''stalk" by a considerable interval, and comes to lie slightly 

 in front of the middle of the thalamencephalon and above the 

 paraphysis, which is now represented by a mass of convoluted 

 tubules, intermingled with blood-vessels, lying between the roof 

 of the thalamencephalon and the parietal eye. 



The " stalk " of the parietal eye has elongated considerably, 

 and its lumen has become obliterated at its point of attachment 

 to the brain. Immediately in front of this point the superior 

 commissure^ has developed. 



In the parietal eye itself the " lens " has become very sharply 

 marked off from the rest of the wall, which latter now forms 

 an optic cup clearly differentiated into two layers. In the 

 inner layer, next to the cavity of the eye, pigment has been 

 deposited between the cells, while towards the close of the stage 

 ' Erroneously termed the " posterior " in my preliminary notes (4, p. 442), 



