ARTHROPODA 183 



forced into the ground, then separated, forming a pit for the reception 

 of the eggs. 



The Digestive System. — From the anterior mouth a short rather 

 broad esophagus (Fig. 84) extends dorsally and posteriorly into the 

 thorax, where it enlarges to form a thick-walled a-op or ingluvies, 

 which extends through the mesothoracic and metathoracic segments. 



On each side of the anterior end of the crop are delicate branched 

 salivary glands which communicate by means of salivary ducts with 

 the mouth cavity. The proventriculus is not constricted from the 

 crop, but extends a short distance to the stomach. The stomach 

 or ventriculus extends to the seventh abdominal segment. At the 

 point where the ventriculus originates, there are eight cylindrical 

 pouches, the gastric cecat, extending anteriorly on the sides of the 

 proventriculus and continuing as eight diverticula or c&c?if^ posteriorly 

 along the sides of the ventriculus. No liver is present. The ileum^ 

 or intestine which has noticeably hardened walls, is found in the 

 seventh, eighth and ninth abdominal segments, constricting poste- 

 riorly as it enters the colon or hind intestine, which runs dorsally 

 down the ninth and tenth segments. The rectum is a small white 

 enlargement situated in the dorsal portions of the ninth and tenth 

 segments and emptying at the anus on the lower surface of the 

 eleventh tergum. 



Respiratory System. — In the grasshopper there are two pairs of 

 thoracic stigmata or spiracles. Eight pairs of abdominal spiracles 

 are situated laterally just above the pleurons, the most conspicuous 

 being the pair found on the anterior margins of the tympani. Ex- 

 tending throughout the body, we find a well-developed system of 

 tracheal tubes, which take the place of the complicated circulatory 

 system found in some other invertebrates, but lacking in the Arthro- 

 poda. 



Circulatory System. — The heart is a long, narrow vessel, extend- 

 ing in the dorsal portion of the abdomen. It is divided by valves 

 into chambers, the anterior one being called the aorta. There are 

 no arteries or veins, but the blood passes through sinuses and finally 

 enters the heart through lateral ostia. (Many of the strongest 

 cardiac poisons have no action whatever on the insects.) 



Urinary System. — The Malpighian tubules are masses of fine 

 tubes, anterior to the rectum, and open into the intestine. They 

 are primitive kidneys. 



Reproductive System. — The ovaries consist of a long white struc- 



