40 H. M. BERNARD. 



particular case. Fui'tlier, as in tlie case of the retina^ these 

 migrations may have considerable influence on the tectonics 

 of the organs in which tliey can be establislieJ. 



Paet IV. 



On the Vesicular Swellings at the Tips of the 

 ''Cones'^ and some Earlier Form-phases in Rod- 

 production in the Amphibia. 



As was shown in Part 1/ the tips of the young cones swelled 

 in!o vesicles on reachingthe pigment layer. Vesicles or parts 

 of vesicles Avere figured (PI. 3, figs. 2,3, and 10), and these justi- 

 fied the construction of the series of form-chang-es shown in 

 tlie ditigram (fig. 4), but they were only certainly seen in eyes 

 fixed with boiling corrosive sublimate. Other figures on the 

 same plate (e.g. fig. 12, and on PI. 31, Part 11/ fig. 29) 

 showed no traces of any such vesicular tips, and in some 

 cases it was difficult to understand why, if they had existed, 

 they should vanish so completely from the sections. This 

 point has now been settled, not, I regret to say, by the 

 discovery of a neAv and more perfect fixative, but by a kind 

 of good fortune. I brought down a few tadpoles from 

 Table Mountain, Cape Town, killed and fixed them in 

 Perenyi's fluid at midnight, i. e. when the pigment would 

 be retracted. The object was to see whether, owing to the 

 brilliant sunlight of South Africa and the intense heat, the 

 pigmentation in the retina showed any modifications on that 

 seen in our indigenous tadpoles, and if so whether any 

 correlated changes in the retina could be discovered. For 

 the same reason I made special efforts to obtain baboon's 

 eyes (see Part V) . 



One interesting difference was at once apparent. The 

 pigment in the South African tadpoles is far greater in 



• This Journal, vol. xliii, I'JUO, p. 23. 

 - Ibid., vol. xliv, I'JOl, p. 4i;}. 



