EEPORT ON THE ISOPODA. 25 



Strolis hromleyana. — That portiou of the chitiuous integument that covers the eye 

 is modified and differs from the rest by its comparative thinness, and by the absence of the 

 characteristic scale-like sculpturing ; corresponding to each element of the eye is a thicken- 

 ing of the cornea, which is, however, very slightly developed in comparison witli other 

 species, and indeed the two surfaces of the cornea appear in transverse section to form two 

 nearly straight parallel lines, the lower surface alone showing a series of undulations of 

 unequal extent. PL X. fig. 5, and PI. IX. fig. 2, represent transverse sections through 

 the cornea of Serolis hromleyana and Serolis schythei respectively ; the conspicuous 

 corneal lenses of the latter type are iu very marked contrast to the feeble indications 

 of these structures in Seivlis hromleyana. 



The tissues of the eye itself have evidently undergone considerable degeneration, and 

 this, coupled with the fact that the specimens were by no means well preserved, renders 

 any satisfactory comparison of their structure with that of the shallow-water species of 

 Serolis and the Arthropoda generallj^ extremely difiicult. I describe the facts as they 

 appear to me. 



PI. X. fig. 5 is a diagrammatic representation of a transverse section through the eye ; 

 beneath the cornea are a series of more or less cup-shaped masses of unequal size and of 

 a granular appearance ; occasionally several of these bodies appeared to have become fused 

 together at their upper extremity, and in a few instances a short upward prolongation of 

 the subjacent tissue into the substance of the body gave it the appearance of being 

 originally formed out of two separate halves ; the granular yellowish coloured matter of 

 which these structures consist is almost entirely unafi"ected by carmine, which stains deeply 

 the surrounding tissues, and is only slightly stained by hsematoxylin. In teased pre- 

 parations of the eye these structures are easily separated, and are seen to have an oval 

 contour ; from their position they would appear to correspond to the vitreous body, and 

 in their general characters recall the vitreous bodies of the type of eye termed by 

 Grenacher " pseudoconous." The compound eyes of the Arthropoda have been arranged 

 by Grenacher^ into three groups — (l) euconous eyes, (2) aconous eyes, and (3) pseudo- 

 conous eyes. In the first group the cells lying behind the facets secrete in addition to 

 it a highly refractive vitreous body or " Kristallkegel," which is composed of as many 

 segments as there are cells ; in the second group the cells remain unaltered and secrete 

 no vitreous body ; in the third group these cells secrete " a soft fluid or semifluid 

 substance " which represents functionally the vitreous body of euconous eyes. It seems 

 to me very possible that the granular appearance of the vitreous body in the deep-sea 

 Serolis has been caused by the coagulation (by alcohol) of a semifluid substance. 

 Pseudoconous eyes, which according to Grenacher are only to be found in the order 

 Diptera, are further distinguished from euconous eyes by the fact that the nuclei of 

 the cells of the vitreous body (the so-called " nuclei of Semper ") remain helow the 



' Sehorgan der Artliropoden, Gdttingen, 1879. 

 (zooL. cn.vLL. EXP. — PART xsxiii. — 1884.) Kk 4 



