Structure of Polycheles sculptus. 



271 



Kff. 2. 



4s 



The dorsal surface of the ophthalmic lobe is smooth, calca- 

 reous, and opaque, and on a level with the adjacent surface of 

 the carapax, except posteriorly, where a small oval area of the 

 extremity of the lobe is exposed by the depression in the 

 carapax. This oval area is thin, semitranslucent, and not 

 calcareous, and has every appearance of being a true corneal 

 area, although I am unable to de- 

 tect any evidence of facets. The 

 carapax along the margins of the 

 sinus is in close contact with the 

 ophthalmic lobe, but is not really 

 connected with it. From the 

 lower portion of each ophthalmic 

 lobe there is an elongated, cylin- 

 drical and somewhat conical, but 

 obtuse and pointed, protuberance, 

 of which the base rests in a trans- 

 verse groove in the base of the 

 antenna, while the terminal por- 

 tion extends well across the open 

 ventral side of the orbital sinus. 

 Upon the obtuse extremity of this 

 protuberance there is a nearly cir- 

 cular area, similar to the cornea- 

 like area at the posterior extremity 

 of the dorsal part of the lobe. 



Unfortunately the specimen is 

 not in sufficiently good condition to 

 enable me to determine positively 

 in regard to the structure of these 

 cornea-like areas ; but that they are connected with the optic 

 nerves and are sensitive to light, there is, I think, no chance 

 for reasonable doubt. While it seems probable that all four 

 of these areas are really faceted like the eyes of ordinary 

 Podophthalmia, it is possible that they may be large, simple 

 or nearly simple eyes, like the eyes of some Amphipoda and 

 Cumacea. The division of the ophthalmic lobe on each side into 

 two or more " eyes " has not, I think, before been noticed 

 among the Decapoda, and is certainly an interesting fact in 

 morphology; but it is apparently not a character of much 

 systematic or phylogenetic value. Among the_ Schizopoda, 

 the lamellar expansion of the ophthalmic lobes in Amblyops, 

 and their broad expansion and partial union in Pseudomma, 

 are quite as remarkable and apparently somewhat similar 

 modifications ; and Ampelisca and Biblys, among the Amphi- 

 poda, are cases in which there are two simple eyes on each side, 



19* 



Ventral view of the anterior 

 portion of the right side of the 

 carapax : a, tubular process 

 containing the canal from the 

 green gland ; b, process of the 

 ophthalmic lobe ; 

 the first pereiopod. 



base of 



