242 AN INTRODUCTION TO ZOOLOGY 



faces are never voided within the hive if the bees are kept under 

 proper conditions. 



THE SALIVARY GLANDS. There are two pairs of salivary 

 glands, one within the head, the other within the thorax. Those 

 in the head lie against the posterior walls of the cranium. The 

 other pair lie in the ventral part of the anterior half of the thorax. 

 Both pairs of glands produce weakly alkaline secretions which are 

 poured out upon the labium where they act upon the food taken 

 through the proboscis (Snodgrass, 1910). 



THE EXCRETORY ORGANS. The Malpighian or urinary tubules 

 (Fig. 134, bl.) are a number of long, fine, hairlike structures which 

 open into the anterior end of the intestine. They were discovered 

 by and named after the great Italian anatomist Malpighi. Ex- 

 cretions are taken from the blood and the fat body in the form 

 of urates; they pass into the intestine, and thence out of the 

 body. 



THE VASCULAR SYSTEM. The blood of the honeybee is similar 

 to that of the crayfish. It is a colorless plasma containing ame- 

 boid corpuscles. It differs in one important point from the blood 

 of most other animals it does not carry very much, if any, 

 oxygen. The distribution of oxygen is accomplished by the 

 respiratory system, as we shall see later. 



An even less complete system of blood -vessels is present than 

 in the crayfish. The principal organ of circulation is the dorsal 

 vessel, or heart (Fig. 134, d.v.). This is a tube lying in the median 

 line just beneath the dorsal surface; it is closed near the posterior 

 end of the abdomen, but opens in the head. The walls of the 

 heart are muscular, and contract at intervals. Blood enters 

 through five pairs of ostia, one pair to each of the five compart- 

 ments or -ventricles (v) into which the heart is divided. Valves 

 prevent the flowing back of the blood, so that each contraction 

 sends a stream toward the head. From here it passes through the 

 spaces among the tissues, finally reaching the ventral parts of the 

 body. Beneath the heart is a horizontal diaphragm of muscle, 

 which forms a pericardial sinus. By contracting, this diaphragm 



