1895.] Dr Rivers, On Binocular Colou7'-mixture, 27*7 



has more recently advocated its existence, but his results were 

 criticised by Hess^, and the latter has described experiments which 

 go far towards disproving the occurrence of unequal accommoda- 

 tion sufficient to overcome a difference of as little as •25 D between 

 the two eyes. 



From observations I have made, it seems possible however that 

 the refractive condition of the eyes may influence results in 

 another way. I see binocular mixture better with my abnormal 

 refraction uncorrected, and better still when my myopia is in- 

 creased by convex glasses. Others who have made observations 

 for me have seen the mixture better when their normal vision 

 has been made artificially myopic or hypermetropic by convex 

 or concave glasses. The improvement seems to depend on dimi- 

 nution of the rivalry of the visual fields owing to blurring of 

 outline, and it is possible that neglect to take account of the 

 refractive condition of the eyes may be one cause of the difference 

 of opinion, and in the accounts of the experiments of most of 

 the observers I mentioned at the beginning of this paper. I 

 have been unable to find any reference to the refraction of their 

 eyes. The influence already considered of difference of focus 

 for different colours would be most marked in those whose re- 

 fraction was normal. 



Some observers, as Volkers^ and Chauveau^ on the other hand 

 have insisted on equality of the two eyes as a necessary condition 

 of success. Chauveau equalised the two eyes by placing before 

 each five plates of white glass 1 mm. in thickness. He found 

 this sufficient in most cases to correct any slight difference be- 

 tween the two eyes ; and, when not sufficient, he removed one 

 or more of the plates from one side. Chauveau was obviously 

 doing more than equalising the two eyes, and may have been 

 favouring mixture by blurring outline, and thus diminishing rivalry 

 in the way I have suggested above. 



(2) On a new Parasite probably allied to Echinorhynchus. By 

 A. E. Shipley, M.A., Christ's College. 



The specimens described came from the skin of a bird Hemigna- 

 thus procerus, taken by Mr Perkins in the Island of Kauai, one of 

 the Sandwich Islands. 



The body of the parasite consisted of three well-marked regions, 

 (i) the head which was pitted and reticulated in a characteristic 

 manner, (ii) the collar, and (iii) the trunk. No spines or hooks 

 were found in the head, but it is possible a hooked proboscis may 

 have been left behind in the skin of the bird. 



1 Archivf. Ophth., Bd. xxxv. Abli. i. S. 157. 



2 Archiv f. Anat. u. Phys. 1838. S. 60. ^ loc. cit. 



