4 HOYLE, PterygiotetitJiis margaritifera. 



lens is the last of the whole group {og). Most of the 

 organs are dull greyish in colour, but some of them have 

 a lustrous appearance, with a play of prismatic colours, 

 and under a lens the surface looks as though divided into 

 a number of facets something like the compound eye of 

 an insect, though, as will be seen from what follows, the 

 resemblance is merely superficial. I have examined 

 sections of several of these and will describe in the first 

 instance the structure of one of the larger ones. 



The largest ocular organs are the one directly in front 

 of and the one immediately below the eye ; they are 

 spheroidal in form and measure, rather more than imm. in 

 diameter. As regards structure, each may be divided into 

 the following parts : — 



1. The Capsule. 



2. The Posterior Cup. 



3. The Inner Cup. 



4. The Central Mass. 



5. The Internal Cone. 



6. The Anterior Cap. 



1. The capsule {Fig. 3, <:.) is about 0-05 mm. thick, and 

 consists of connective tissue : in the outer layer are fibres 

 and cells intermixed, whilst the deeper layer consists almost 

 entirely of fibres disposed parallel to the surface. To- 

 wards the equator of the organ this layer becomes some- 

 what thicker and gradually merges into the loose areolar 

 connective tissue in which the organ is embedded. 

 Outside the capsule is a membrane composed of a single 

 layer of columnar cells, with spheroidal nuclei i^Fig. 3, /;.), 

 which has the appearance of parenchymatous cartilage 

 and is, doubtless, the exterior layer of the eyeball seen in 

 section. 



2. The posterior cup {Fig. 3,/.f.) is of very remarkable 

 appearance : in a median section of the organ it is seen to 



