15° FIRST LESSONS IN ZOOLOGY 



The cephalothorax is covered above and on the sides by 

 the carapace, which is divided by a transverse hnc into a 

 front part or head and a hinder part or thorax. At tlie 

 anterir)r end of the liead is a sharp projection, the ros- 

 trum. Where is the mouth .'' Where are the eyes .■" 

 Rcmo\'e one of the e)'es and examine its outer surface 

 with a microscope. A bit of the outer wall should be 

 torn off and mounted on a glass slide. Note that it is 

 made up of a great many little facets placed side by side. 

 Each of these is the external window of a single eye ele- 

 ment or ommatidium. An eye composed in this wa}' is 

 called a compound e}-e. (See accounts of the compound 

 eyes of insects on pp. 22 and 112.) Make a drawing of 

 the surface of part of an ej-e. In front of the ej'es note 

 two pairs of slender many-segmented appendages. The 

 shorter pair, the antennules, are two-branched. Remove 

 one of them and note at its base a small slit along the 

 upper surface. This opens into a small, bag-like structure 

 which contains fine sand-grains. The bag is protected by 

 a series of fine bristles along the edge of the slit. The 

 structure is believed to be an auditory or hearing organ. 

 The longer pair of appendages are the antenn.ne, and in 

 the fine, hair-like projections upon the joints is believed 

 to be located the sense of smell. Beneath the basal 

 portion of each antenna there is a fiat, plate-like projec- 

 tion, at the base of \\'hich on the upper edge will be noted 

 a small opening, the e.xit of the kidne)', or green gland. 



Stick one point of the scissors under the posterior end 

 of the carapace on the right side, and cut forward, thus 

 exposing a large cavity, the gill-chamber. Remove all 

 of the mouth-parts, legs, and abdominal appendages from 

 the riglit side, being careful to leave the fringe-like parts, 

 the gills, attached to their respective legs. Place all of 

 the appendages in order on a piece of cardboard. 



Examine the abdominal appendages, called pleopods, 



