LATERAL AND CENTRAL EYES OF SCORPIO AND LIMULUS. 179 



Nevertheless, Graber has the merit of having, as we shall 

 mention below, correctly observed some important facts as to 

 the Scorpion's retina — for the first time. In reply to Graber's 

 article, Grenacher has published a memoir in which, whilst he 

 very justly rejects the " corrections " attempted by Graber, he 

 gives an account of certain observations on the structure of 

 the Scorpion's eye — made in order to control the statements of 

 Graber. Unfortunately these observations of Grenacher were 

 confined to the central eye, and did not extend to the very 

 differently-built lateral eye; and moreover, the observations 

 are not illustrated by any figures. We shall not have occasion 

 to refer to them again, since they merely furnish the observa- 

 tional basis which enabled Grenacher categorically to deny 

 some of Graber's assertions. 



Both this paper of Grenacher's and that of Graber, to which 

 it is a reply, deal very largely with the eyes of Myriapods ; 

 and the structure of these, though not of those of the Scor- 

 pion's, is beautifully illustrated in Grenacher's plates. 



Hence it is actually the case that no figures, except the very 

 erroneous ones of Graber, have been published of the eyes of 

 Scorpions J whilst the structure of the lateral eyes of those 

 animals has not been looked at by the most capable student of 

 the Arthropod eye. 



With regard to Limulus, there is practically nothing else 

 published relating to the structure of the eyes than the results 

 given by Grenacher in his large book, of the examination of 

 the lateral eye of a not too well preserved specimen. No one 

 has given any account of the minute structure of the central 

 eye of Limulus. 



It is true that Dr. Packard has alluded to this matter in 

 his memoir on the " Anatomy, Histology, and Embryology 

 of Limulus," but it is so abundantly evident tbat Dr. Packard 

 has not made use of the ordinary methods of histological in- 

 quiry in dealing with this and other parts of the King-crab, 

 tbat it seems to be the proper course to omit any further refer- 

 ence to the drawings and descriptions in his memoir which are 

 supposed to have reference to the histology of the central and 



