290 S. WATASE. 



a. Sa-olix. 



(Pigs. 1,1a, li, 3, PI. XXIX.) 



The crcncral structure of the eyes of Serolis has already been 



made known by Beddard.* Althou-h I have verified all the 



chief results of his research, I shall speak of a few details Nvhu^h 



seem to me siiecially significant. 



The cells of the ommatidiuni are arranged in three principal 

 strata, a, h, c (Fig. la, PI. XXIX). Each stratum of cells is 

 characterized by the special product which it secretes, viz. 1, 2 

 and 3. , - 



The outermost stratum (a) secretes upon its external surface 

 the chitin which constitutes the cornea or the corneal facet {c, 

 Fig. 1, PI. XXIX). 



The cells themselves have been designated as the corneagen by 

 Patten.^ . 



The corneagen is sometimes difficult to detect in the eye ot 

 the adult animal and may easily be overlooked. It is very 

 conspicuous in the young. 



The next stratum of cells (5) is also characterized by the 

 chitinous secretion on the surface nearest the median axis of the 

 ommatidium. The two cells {b) secrete a thick chitinous layer 

 which encloses an ovoidal space of considerable size filled with a 

 transparent liquid substance, (2). The cell (h) has been named 

 vitrella (Lankester and Bourne);' and the oyoidaj chitinous body. 

 (2) is the crystalline con^ (c. c, Fig. 1, PI. XXIX.) 



'Beddard, P. K. Challenger Report, Zoology, Vol. XI, Isopoda: SeroUdae. 

 His additional observations on Serolis may be found in the paper by the same 

 author, On the Minute Structure of the Eye in Cymolhoidae, Trans. Roy. boc. 



^%udieion the Ey>:s of Arthropod: I. Development of the Eyes of Vespa, 

 u-ith ohxervations on the Ocelli of some Insects, p. 193, .Tournal of Morphology, 

 Vol. I, No. 1, 1887. 



s The Mmute Structure of the Lateral and the Central Eyes of Scorpio and 

 Limulus. Quart. Jour, of Micro. Science, Vol. XXIII, p. 198, 1883. _ 



'• Vitrella " is synonymous with " retinophora " of Patten ; '• vitreous cell 

 and " crystalline cone cell " of authors. The nucleus of the vitrella has been 

 named byClaparOde "Scmper's nucleus," attel- its discoverer : Zur Morphologic 

 der zHsammengeseizten Augen bei den Arthropoden. Von Edouard Claparedo. 

 Zeit. t. Wiss. Zool. Bd. X. p. 193, 1860. 



* It is interesting to notice that the observations made by Clarke on the eye of 

 aTrilobite {The Structure and Development of the Visual Area in the Tnlobile, 



