144 Structure and Functions of Eyes of Arthropoda. [Apr. 12, 



and resolved into a reddish granular precipitate and a transparent 

 fluid, which mixes readily with water and saline solutions ; it is 

 blackened by osmic acid, and rapidly dissolved by ether, oil of cloves, 

 and, though less rapidly, by alcohol. 



A subcorneal lens has long been recognised in the eyes of Isopods, 

 and has been regarded as a modified crystalline cone. Miiller believed 

 a similar lens to be present in the compound eyes of some insects. 

 Of late this lens has been overlooked ; I have, however, found that it 

 really exists in the majority of Arthropods. It consists of the 

 oil-like fluid just spoken of, enclosed in an elastic capsule. It gives 

 the Cornea the peculiar brilliancy which it posseses during life. The 

 fluid contents of the lens is permeated by a more or less dense stroma, 

 which, when the oil is rapidly dissolved, by reagents, splits into four 

 parts. These are the bodies described by Claparede as " Semper' s 

 nuclei.'''' 



In some insects the lens can be isolated, and its capsule can then 

 be ruptured by pressure on the thin cover-glass, so that the escape of 

 the fluid can be actually observed. The empty capsules are then 

 seen to be finely wrinkled, and usually torn by a single fissure. 



In some insects the lens is developed from the cornea, in others 

 from the outer portion of the crystalline cone. 



The Spindles of the Great Rods also consist chiefly of the same 

 refractive fluid, hence the profound modifications which they undergo 

 when disturbed for purposes of investigation, or even as the result of 

 post mortem change. 



The formation of a subcorneal image as well as that of an erect 

 image on the retina is discussed in this part of my paper, and the 

 theory is shown by measurements to be in harmony with the actual 

 conditions which have been observed. 



The remainder of this part of my paper is occupied by a consider- 

 ation of the principal modifications of the Dioptron. 



I have recognised four distinct modifications of the Cornea, three 

 of which exist in different stages of development in the cockroach. 

 I have named these modifications, 



I. Simple Continuous Cornea. 



II. The Facetted Cornea. 



III. The Kistoid Cornea. 



The fourth modification is apparently confined, amongst insects, 

 to the imago condition in the Gnats ; in these the cornea consists of 

 the crystalline cones of the nymph united to each other by a thin 

 cuticular lamina. I have used the term lenticular to distinguish this 

 form of cornea. 



I have incorporated such knowledge as I have been able to glean 

 with regard to the development of the cornea and subcorneal lens 

 with this section of my paper. 



