366 MR. F. E. BEDDARD ON THE STRUCTURE [May 6, 



of the Serolidae and the Cymothoidae, which was published in the 

 ' Transactions.' The present paper is a continuation of the same 

 subject, but deals with the genus Arcturus. The material, like that of 

 my former paper, consists of teased preparations and of sections of the 

 eyes of species obtained during the voyage of H.M.S. 'Challenger,' 

 all of which species have been described by me in my Report (3). 



In my paper on the structure of the eye in the Cymothoidae, I 

 mentioned the principal papers dealing with the Isopodan eye, which 

 are not many in number. Since the appearance of that paper but 

 little has been published upon the Isopodan eye. lam, indeed, only 

 acquainted with a single memoir upon the subject, one by Mr. S. 

 Watase (11); this paper deals largely with Serolis, but it contains 

 also some very weighty observations upon the morphology and 

 pedigree of the Arthropod eye in general. 



It is gratifying to me personally to find that Mr. Watase has 

 "verified all the chief results" of my own research. This fact 

 also gives me greater confidence in laying tlie present paper before 

 the Society. If the state of preservation of the specimens of Serolis 

 was so good as to enable me to state accurately the principal facts 

 in the anatomy of the eye, it seems likely that the Arcturi, which 

 were preserved in an identical fashion, will also furnish reliable data. 

 In any case our knowledge of this particular genus is at present, so 

 far as I am aware, absolutely nil ; and it is almost unnecessary to 

 state that the deep-sea forms are as little known as those which in- 

 habit the shallower waters. Mr. Watase, in his description of the 

 eye of Serolis, which occupies the first five pages of the special part, 

 refers to the presence of a "corneagen" ^ (a term introduced by 

 Patten, 13) below the cornea and above the cells of the vitrella ; he 

 also figures a row of pigmented cells surrounding the vitrella ^. 

 These structures were not figured or described by myself, but I am 

 not prepared to dispute the probable justice of Mr. Watase's addition 

 to my own account. 



It seems to me to be very probable that this corneagen layer is, 

 as Patten has particularly insisted, always present in eyes of these 

 types ; and Watase has shown a very strong raison d'etre for its 

 presence. 



The present paper, however, only professes to be a very small 

 contribution to the morphology of the Isopodan eye ; the main 

 object is to compare the minute strVictue of the eye of species liviug 

 iu shallow water with thai of their deep-sea allies. 



The questions involved are interesting and lead to some rather 

 important conclusions about the life of these deep-sea forms. 



Iu the first part of my ' Challenger ' Report, dealing only with the 

 very remarkable genus Serolis (2), I gave some figures and a brief 

 description of the structure of the eyes in two deep-sea species, viz. 

 Se?'olis bromleyana and Serolis necera. Without recapitulating all 

 the results here, I may point out that the eyes in those forms showed 

 very considerable traces of degeneration ; this degeneration was 



1 PI. xxix. fig. 1 ry, fig. P n. 



- This term was introduced by Laukester and Bourne. 



