1026 CRUSTACEA. 



3. A pair of simple eyes consisting of an internal prolate lens 

 situated at the extremity of a vermiform mass of pigment, and of a 

 large oblate lens-shaped cornea. The cornea is connected intimately 

 with the exterior shell of the front or under side of the head (figures 

 6 and 15, Corycceus; 7, Sappliirina) , and the two corneae are like 

 spectacles adapted to the near-sighted lenses within ; their size is 

 extraordinary, being often one-third the greatest breadth of the body 

 in Cory casus. The lens (I, fig. 15) and the cornea (c) are often very 

 distant from one another, being separated by a long clear space. The 

 exterior 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 pene- 

 trated 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. Other figures and illustrations are given 

 among those of the Corycaeidse. 



Antennce. — There are two pairs of antennas in all the Cyclopoidea. 



a. First pair of antennae. — The first pair of antennae is always 

 antenna-like in form and function in females ; in males one or both 

 are sometimes prehensile, for clasping the female in coition. The 

 organs are either simple (figs. 16 to 41, Plate 70), or appendiculate 

 (figs. 42, 43*). The number of joints varies from three to twenty-four, 

 and perhaps, twenty-eight. 



When appendiculate, there is a basal portion, consisting of two to 

 iive [rarely] joints; and this base bears at apex a slender flagellum, 

 three- to seven-jointed, besides a small one- or two-jointed appendage 

 or branch, which usually terminates in two setae. 



The figures 16 to 43, illustrate the principal varieties of these 

 organs. They show that the few-jointed antennae are sometimes 

 short (figs. 16-18), and sometimes long; and farther, that in the 

 same genus, antennae of equal length, may consist of seven or twenty 

 joints : also, in the same species, a male antenna may have but half 

 the number of joints in the female, although scarcely different in 



* Figs. 16, 17, from Sapphirina and Corycseus; 18 a, b, 19, 20, Cyclops; 21, Calamis; 

 22?, 23 $, 24, Euchajta; 25, Undina; 26, 27, 28, 29, Ponfcella; 30 to 36, Pontella; 37, 

 38, Candace; 39, 40, Oithona; 41, Acartia; 42 a?, b t } Clytemnestra ; 43, Setella. 



