26 BULLETIN OF THE 



The Innervation of the Retina. 



The study of the termination of the nerves in the retina is of partic- 

 ular importance, since it affords a means of identifying the perceptive 

 elements. Wherever these elements may be, the ultimate branches of 

 the nerve-fibres must unquestionably lead to them ; hence the impor- 

 tance of discovering the termination of the nerve-fibres. 



Students who have investigated the compound eyes of Arthropods 

 have held two opinions as to the position in which the nerve-fibres ter- 

 minate. One school has maintained that the fibres terminate in the 

 crystalline cones, and that therefore these bodies are the perceptive 

 elements. The other school has endeavored to show that the fibres 

 end in the region of the rhabdome, and that for this reason the rhab- 

 dome is the perceptive element. I shall not attempt to give an his- 

 torical account of this subject, but only call attention to the fact, that 

 of late years the majority of writers have expressed the opinion that the 

 rhabdome is the perceptive element, and that the cone is merely dioptric 

 in function. This conclusion has been recently criticised by Patten, 

 who believes the cone to be the perceptive body. 



Many of Patten's statements are based upon observations which were 

 possible only by his methods of investigation. On this account, as well 

 as for the reason that his paper is the most important recent contribu- 

 tion to the study of nerve-termination in compound eyes, I shall not 

 refer to the older publications, but limit myself to what he has pre- 

 sented in his article on " Eyes of Molluscs and Arthropods," and to such 

 papers as have appeared since the publication of that work. 



When comparing Patten's statements on nerve-termination with 

 those of other recent investigators, I was inclined to believe, since 

 Patten used new and probably better methods of study, that his results 

 were more trustworthy. The contrast between his views and those 

 which are more generally accepted is so striking, however, that in begin- 

 ning a study of the nerve-terminations the first step to be taken was 

 necessarily one of confirmation. I was unable to obtain the same 

 species of Crustaceans as Patten had used, but I believe that I was safe 

 in assuming that the difference which may exist between the innerva- 

 tion of the retina in Penseus and Homarus could not be a fundamental 

 one, and that the more important feature which had been demonstrated 

 in one genus could be shown in the other. I consequently prepared 

 sections of the retina of Homarus according to the methods which Patten 

 had recommended, and although I was careful in both preparation and 



