102 LABORATORY STUDIES IN ZOOLOGY 



The coxopod (jf the maiulihle is greatly elongated transversely 

 to form a strong functional jaAv. The hasipod possesses a much 

 reduced two-jointed endopod which forms the palp. The exopod 

 is lost. In front of the mouth opening is the upper lip or labrum. 



The protopod of the antenna is two-jointed, the coxopod being 

 small and bearing the aperture of the duct of the renal gland, 

 while the basipod is larger. The long many-jointed filament 

 connected with the basipod by two stout basal segments is the 

 endopod. The thin, sharp projection near the base of the filament 

 is the exopod. 



Draw the left antenna enlarged about three times. 



The antenmde possesses a three-jointed protopod, from which 

 arise two, short, many-jointed filaments. These may or may 

 not represent the endopod and exopod. It is perhaps doubtful 

 whether this appendage is strictly comparable with the others. 



This study shows that there are at least 5 pairs of appendages 

 borne upon the head, 8 upon the thorax, and 6 upon the abdomen, 

 making a total of 19. If the eye stalks are construed as belonging 

 to the same category of appendages as the others and, therefore, 

 representing a segment, and the telson accorded the rank of a 

 segment, then there are represented in the body of the crayfish 

 21 segments. 



Class Insecta : The Lubber Grasshopper , Schistocerca americanum 

 (or an Allied Species). — One of the Southern species of grass- 

 hopper is chosen for study because of its large size. Most of our 

 grasshoppers, so common in the summer and autumn, show the 

 same fundamental plan of structure but are difficult of study 

 because of their small size. 



External Structure. — Study a specimen in a dissecting pan. 

 A chitinous exoskeleton, lacking the lime deposits of the crayfish, 

 is present and is secreted by the ectoderm lying beneath. The 

 hard surfaces of the exoskeleton are known as sclerites, which are 

 joined by sutures less densely chitinized. 



Regional Differentiation. — Note that the bilaterally sym- 

 metrical body is divided into three distinct regions; the movable 

 head, the thorax bearing legs and wings, and the conspicuously 

 segmented abdomen. 



The Head and Its Appendages. — The head exhibits no clear 

 evidence of segmentation. The six segments (at least) which it 

 comprises are suggested by comparative structural studies. 

 The larger part of the head is enclosed in a single sclerite, the 



