202 EVENINGS AT THE MICEOSCOPE. 



out expressly for tliem in the front margin of the 

 shell. 



If ever you should chance to meet with the exotic 

 Crustacea of the genera Corycwus and SapjpJiirina, joxi 

 would see a form of eye of a quite remarkable and 

 unique character. It is described by Dana in the fol- 

 lowing terms : — 



" A pair of simple eyes consisting of an internal 

 prolate lens, situated at the extremity of a vei'miform 

 mass of pigment, and of a large, oblate lens-shaped 

 cornea. The cornea is connected intimately with the 

 exterior shell of the front or the under side of the head, 

 and the two cornese are like spectacles adapted to the 

 near-sighted lenses within ; their size is extraordinary, 

 being often one-third of the greatest breadth of the 

 body in Corycmus. The lens and the cornea are often 

 very distant from each other, being separated by a 

 long clear space. The external surface of the cornea is 

 spherical ; but the inner is conoideo-spherical, or para- 

 bolic. The texture is firm, and when dissected it 

 breaks or cuts like a crystalline lens. The true lens is 

 always prolate, with a regular contour, excepting be- 

 hind, where it is partly penetrated by the pigment. 

 The pigment is slender, vermiform, of a deep colour, 

 either red or blue, but at its anterior extremity usually 

 lighter, and often orange or yellow." * 



We might find much more both instructive and 

 amusing in examining microscopically the structure of 

 the higher Crustacea ; but we will now dismiss them 

 in order to discuss some of the lower forms, many of 

 which are so minute that their whole bodies may be 

 watched with ease performing all the functions of life, 



* Rep. on Crust, p. 1026. 



