68 BULLETIN OF THE 



While the existence of a pre-retinal membrane, as claimed by Graber, 

 is corroborated for eyes of the " pre-nuclear " type, and its presence made 

 readily comprehensible by the observations of Locy, the conclusions drawn 

 by Graber from this anatomical fact have received the reverse of con- 

 firmation. Whether eyes of the post-nuclear type exhibit this membrane, 

 is not so easily determined ; but the question will be considered in a 

 subsequent part of the present paper. 



Lankester and Bourne ('83, p. 182) apply the name " ommateal cap- 

 sule " to that portion of the " basement-membrane " (inner cuticula) which 

 lies in the region of the ommateum * of the lateral eyes of scorpions, and 

 then extend the use of the term | to " diplostichous " eyes, so as to cover 

 what has been called by the earlier writers "sclera." Denying the existence 

 of the separate " vitreous " claimed by Graber for the lateral eyes, they 

 of course find in these eyes nothing equivalent to Graber's pre-retinal 

 membrane. In the central eyes, however, it exists as " a strong lami- 

 nated membrane," forming a septum which divides the vitreous body 

 from the rest of the ommateum. The ommateal capsule, of which the sep- 

 tum, they say, forms a part, is " finely laminated and devoid of nuclei." 



The " ommateal capsule " in the lateral eyes of Limulus (I. c, p. 203), 

 " whilst well marked in every other region, is deficient immediately below 

 the retinula, where the group of optic-nerve filaments passes out of or into 

 the capsule." The authors regard this deficiency of the capsule as related 

 to the intrusion of connective tissue into the eye ; for it is around the 

 optic nerve that the intrusion appears to take place. 



In the central eyes of Limulus they " could not define an ommateal 

 capsule," the intrusive connective tissue being much more abundant than 

 in the lateral eyes ; but a vitreous body composed of short cells is sepa- 

 rated from the retinal body behind it by " firm membrane," not very 

 clearly indicated in their figures, but apparently continuous with the 

 basement-membrane of the hypodermis. 



It seems to me possible that the great difficulties attending the investi- 

 gation of these eyes account for the fact that the authors have not dis- 

 covered a post-retinal capsule. 



* Compare the quotation in the footnote, p. 50. 



t However appropriate this terminology may be for monostichous eyes, it evi- 

 dently is not sufficiently distinctive in the case of " diplostichous " eyes. It would 

 doubtless be better to adopt a terminology which should express the topographical 

 relation of the basement-membrane to the retina. The wJiole capsule might then be 

 called the ^^ retinal capsule." In diplostichous eyes the "sclera" could then be 

 called the peri-retinal (or better, perhaps, the post-retinal) membrane, in contradis- 

 tinction to the remaining portion, already appropriately named by Graber " pre- 

 retinal membrane." 



