Anatomy of Daphnia. 247 



place of the " barbillons" of the female, and are each composed 

 of four rings ; the first of which is very long, a little arched, 

 and has at its extremity a " talon " from which issue two stiff 

 hairs. The second and third are very small, whilst the fourth 

 is a long horny hook. They seem to assist the first pair of 

 feet in the act of copulation. The eye (plate ix. fig. 12.) is a 

 spherical body contained in an infundibuliform tube, allowing 

 of a semi-rotatory motion upon its centre, and is furnished 

 with twenty crystallines according to Straus, which are limpid, 

 and when isolated are each pear-shaped. Swammerdam as- 

 serted that there were two eyes, which seemed to be joined 

 together, and several authors have adopted the same opinion. 

 Schaeffer however says there is only one, and Muller and 

 DeGeer repeat this, an opinion which has also been adopted 

 and proved correct by Straus and Jurine. Eichhorn, as quoted 

 by Straus, asserts that the eye is the stomach of the insect ! 

 On each side upon the base of the head are inserted the rami 

 or arms. They consist each of a single joint at the base, divi- 

 ding into two branches. This first joint is slightly conical, of 

 the length of the head, and very moveable at the base, by 

 means of a joint which unites it to the body and facilitates its 

 motions in every direction. The posterior branch of each is 

 divided into four articulations, the first being very short : the 

 other is divided into three. Both branches are furnished with 

 several long filaments or setae, the posterior branch having 

 none on the two first joints, one at the extremity of the third, 

 and three at the extremity of the fourth. The anterior branch 

 has one at the extremity of each of the first two joints, and 

 three at the extremity of the third. These filaments in some 

 of the species, such as the Pulex, &c. are beautifully feathered 

 or plumose, and are each of them composed of three moveable 

 joints, which, as DeGeer says, augment their flexibility. 

 Swammerdam calls these organs the arms, and describes their 

 motion very particularly, which he says is three-fold : recti- 

 lineal, up and down, and to each side ; unequal, keeping the in- 

 sect now at the bottom and then again at the top of the water, 

 which sort of motion he compares to the flight of a sparrow ; 

 and gyratory, by which the insect moves itself in a circular 

 manner. DeGeer also calls them arms, but Muller, and most 



