128 MANUAL OF ANIMAL BIOLOGY 



selected. There are large muscles, attached to the proximal end of 

 the sheath structure and also to the abdominal wall, which, by 

 their contraction, bring about the movement of the sheath and 

 darts. When the darts have been forced into the tissues, there is 

 an injection through them of poisonous material. The latter is 

 formed in convoluted, tubular structures, the poison glands, 

 which secrete the poison into an enlarged portion of the tube, 

 known as the poison sac. From the sac a tube leads down along 

 the sheath. The poison is composed of an acid and an alkali, each 

 being secreted by a definite region in the poison glands. It is 

 stated that it is generally fatal for the Bee to use the sting, for 

 when the darts and the sheath have been forced into the tissues of 

 the other animal, it is very rarely that they can be dislodged with- 

 out tearing off the posterior end of the abdomen of the Bee. (W. f, 

 218.) 



B. Organ Systems 



The general plan of arrangement of the various organ systems 

 of the Bee is fundamentally the same as described in the study of 

 the Grasshopper. 



1. Nutritive System 



The tubular alimentary canal is differentiated to form a number 

 of interesting structures and is adapted for the intake of both 

 liquid and solid foods. Connecting with the mouth cavity is the 

 esophagus which is a small, undifferentiated tube running from 

 the mouth entirely through the thorax and into the anterior end 

 of the abdomen. Here it enlarges to form the crop, or honey sac. 

 By means of this organ the Bee is able to store temporarily a con- 

 siderable quantity of nectar. When the hive is reached, the nectar 

 in the honey sac is regurgitated and placed in the cells to form 

 honey as described below. 



At the posterior end of the honey sac there is a short, stalk-like 

 connection (proventriculus) which leads into the true stomach 

 (ventriculus) . The proventriculus contains four lips which are 

 regulated by special sets of muscles to open and close them as 

 needed. The stomach is lined with a layer of endodermal cells 

 which secrete the digestive enzymes. Other cells in this lining 

 layer are absorptive, and a certain amount of the digested food is 

 absorbed from the stomach by them and passed into the blood 

 stream. The unabsorbed, partially digested food passes from the 



