INVERTEBRATE ZOOLOGY. 



103 



in a fork (furca) tipped with long plumose bristles. In the center of the an- 

 terior end of the carapace is the eye, a fleck of pigment which gives sensation 

 of light and possibly of color. This eye gave the animal its name, but it is 

 really double, as is seen by its shape. There are two pairs of antennae, of 

 which the first bears tufts of olfactorj' hairs. It is transformed in the male 

 into a clasping organ, used during i^airing. The legs consist of a double basal 

 I)iece and two branches, each consisting of flattened joints. There are no 

 gills. The formula for somites and appendages is as follows. 



Body Regions. Somites. Appendages. 



I I Antj (Clasping in male.) 



Head 



Tliorax 



Abdomen 



II I 



III I 



j \_ 



I IV i 



I I 



I V I 



r VI J 



VII 



VIII 



TX 



X 



11 

 12 



i;; 



Ant. 

 Md 

 Mx, 

 Mx, 



L, 

 L, 



L, 



(Reduced in .size. 



U 



15 



(Witli aims and furca.) 



74. IiiteriKtl ((iiiitoiii!/. The aJ'niu'ntuvji canal is a straight tube in the 

 median line with but little differentiation of parts. Anus in fifth abdominal 

 segment. No accessory organs. During life the canal oscillates continually 

 back and forth, stirring the fluid in the body cavity and thus functionally re- 

 placing a cuTitlatovT/ system, which fails entirely. There is no special respira- 

 tory system. The reproductive organs differ in appearance during different 



