694 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



The whole eye is usually spherical, but in a few species is somewhat 

 elongated diagonally or crescent shaped. 



Each eye is surrounded b}^ a wide blood sinus through which the 

 blood constantl}^ flows, so that the eyes are continually Ixithed in it. 

 The eyes are capa])le of moving inside these sinuses and often show a 

 trembling motion similar to that in other copepods. 



The tactile organs include the two pairs of antenna?, the original 

 tactile function of the first pair being almost wholly superseded by the 

 acquired function of prehension, the basal lobes on the posterior legs, 

 and the long finger papillas beside the opening of the oviduct in the 

 female. There are also tactile setse around the anterior half of the 

 edge of the carapace, and some at least of the accessory organs in 

 the male serve primarily as organs of touch (p. 697). 



Fig. 22.— Semen receptacles anb papillae op Argulus amekicanus female under greater 



ENLARGEMENT, b. /., BaSAL LOBES OF POSTERIOR LEGS; J. d., DUCTS LEADING FROM THE RECEPTA- 

 CLES TO THE PAPILL.E; S.p.. SEMEN PAPILLA; S.r., SEMEN RECEPTACLES; t.p., TACTILE PAPILLA. 



The sexual organs. — The sexes are separate, and the female is usu- 

 ally larger than the male, though there is no such difference in size as 

 among some of the other parasitic forms. And in laticauda the males are 

 actually larger than any females thus far found. The females are also 

 considerably more numerous than the males. 



The female sexual organs consist of an unpaired median ovar}' and 

 paired seminal receptacles (fig. 21). The ovary starts as an unpaired 

 ridge of cells along the right or left side of the intestine. In later 

 development it migrates to the median line, and becomes a simple 

 receptable for holding the maturing eggs. It reaches from the 

 stomach to the posterior end of the thorax, where it narrows abruptly 

 into a short oviduct which opens out at the base of the sinus between 

 the lobes of the posterior logs. In many species there is a long tactile 



