120 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



stigma. How many pairs of stigmata are there on the abdomen? The tergum 

 and sternum of the first abdominal segment are separated from each other by 

 the depression for the insertion of the third legs. The sternum is fused to the 

 sternum of the metathorax, a crescentic suture, however, marking the boundaries 

 between them. The tergum bears upon its sides a circular opening with a 

 chitinous run across which is stretched a thin membrane. This is the organ 

 of hearing, or chordotonal organ, commonly called an "ear." On the anterior 

 border of the ear is the first abdominal spiracle. 



The next seven abdominal segments are all alike and present no new features. 

 The remainder of the abdomen is different in form and structure in the two sexes. 

 In both sexes, the ninth and tenth terga are narrow and more or less fused. From 

 the tenth tergum a broad triangular plate, the suranal plate, extends posteriorly, 

 forming the roof of the anal opening. Whether the suranal plate is a part of the 

 tenth tergum or represents an eleventh tergum is undecided. From the sides 

 of the tenth tergum a pair of small pointed processes projects posteriorly. These 

 are called the cerci or cercopods, and are generally regarded as the appendages 

 of the tenth segment. Under each cercus is a larger triangular plate, the podical 

 plate, supposed by many authors to represent part of an eleventh segment. The 

 anal opening is between the two podical plates. 



In the male there is a broad ninth sternum, followed by a triangular plate 

 curving dorsally, called the subgenital plate, probably representing the tenth 

 sternum. The subgenital plate terminates dorsally in two short spines. 

 Between the subgenital plate and the podical plates is the male genital opening, 

 and the male genital apparatus is concealed under the subgenital plate, which 

 forms a kind of hood over it. Grasp the subgenital plate and pull it backward, 

 revealing the male apparatus ending in a hard point, the penis. 



In the female, the abdomen ends ventrally with the eighth sternum, from 

 which a pointed projection, the egg guide, extends posteriorly. Behind the 

 eighth sternum, terminating the body, are two pairs of hard pointed styles, which 

 together constitute the ovipositor, or egg-depositing apparatus. The female 

 genital opening lies at the base of the egg guide, and will be seen later. There 

 is no doubt that the styles of the ovipositor are true abdominal appendages, 

 homologous with the legs and mouth parts. The grasshopper lays its eggs in 

 the ground. Does this fact suggest to you the function of the styles? 



2. The internal anatomy. The dissection of preserved specimens is rather 

 unsatisfactory. For this reason the student may have some difficulty in locating 

 all of the parts described and should not waste too much time in searching for 

 them. 



Cut out the dorsal body wall in one strip beginning in front of the suranal 

 plate and extending forward to the compound eyes. Remove and preserve 

 the strip without injuring it. A large space containing the viscera is revealed. 

 As in the case of the lobster, this space is not a coelome but is an enormous blood 



