204 EVENINGS AT THE MICROSCOPE 



the front or the tinder 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 Corycceus. 

 The lens and the cornea are often very distant from each 

 other, being separated by a long clear space. The ex- 

 ternal surface of the cornea is spherical; but the inner is 

 conoideo -spherical, or parabolic* 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 behind, where it is partly penetrated by the 

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

 color, either red or blue, but at its anterior extremity 

 usually lighter, and often orange or yellow." 



We might find much more both instructive and amus- 

 ing in examining microscopically the structure of the higher 

 Crustacea; but we will now dismiss them in order to dis- 

 cuss some of the lower forms, many of which are so mi- 

 nute that their whole bodies may be watched with ease 

 performing all the functions of life, while confined under 

 our eye, on the stage of the microscope. I refer to the 

 tiny active little creatures known as Water-fleas, which are 

 abundant in both fresh and salt water. 



In this jar of fresh water, which has been standing in 

 the window for weeks, you may see among the green fila- 

 ments of Chara many little atoms which scuttle hither and 

 thither with a rapid succession of short leaps. These be- 

 long to the genus Cyclops, and are Crustacea, belonging 

 to the order ENTOMOSTRACA. 



By the aid of a glass tube which I stop at one end with 



1 "Rep. on Crust," p. 1026. 



