THE POPULAR INSECT PLAN 



209 



-Salivary glarjcCS 

 esophogors 



- - honay Stomach 

 ..prov©ntricultC5 



Digestion, Circulation, Respiration, and Excretion 



The digestive tract posterior to the crop has to do with the digestion 

 of food. The stomach, a large cyhndrical structure, has a valvelike 

 arrangement between it and the crop to prevent nectar not used as 

 food from going further. It leads into a small intestine, which in 

 turn expands to form the 

 rectinn at the posterior • 



end of the body. - (^'W'^'^ ■ - pl^^'^yn&al glands 



Attached to the an- x% '^-^A<a#-P°stc«nlbml%iands 



terior end of the intestine 

 is a circle of Malpighian 

 tubules, about one hun- 

 dred in number, named 

 after their discoverer, 



Marcello Malpighi, who '^V^^^^^^'^^^-'J^f 

 first pictured them in 

 his Anatomy of the Silk- 

 worm published in 1669. 

 The tubules are excre- 

 tory in nature, as is 

 proven by the fact that 

 small crystals of nitrog- 

 enous wastes are formed 

 in them. 



In the insects and 

 crustaceans, there is no 

 closed system of blood vessels as was found in the earthworm, but 

 in the former there is a well-developed, dorsally placed, tubular 

 heart, located in the abdomen and perforated by paired openings, 

 or ostia, through which blood enters. Blood is forced out of the 

 anterior end into spaces, or sinuses, which in the insects are found 

 throughout the body cavity and take the place of blood vessels. 

 The heart acts somewhat like a rubber bulb syringe in a pail of 

 water, serving, along with the muscular movements of the insect, 

 to keep the blood in motion through the blood sinuses. Snod- 

 grass ^ shows that there is a rapid and complete circulation of 

 blood through the main sinuses, the blood being forced backward 

 into the abdomen on the ventral side of the body by the pulsat- 



smdl intestine 

 ventriculus. 



rectal gkncC 



The food tube of worker bee and glands con- 

 nected with it. The pharyngeal glands form the 

 royal jelly or brood food given to the larvae by the 

 workers. The postcerebral glands secrete a fatty 

 substance, which is thought to be mixed with wax 

 in making honeycomb. The salivary glands are 

 true digestive glands. (After Snodgrass.) 



1 Snodgrass, Anatomy and Physiology of the Honey Bee, McGraw-Hill, 1925, pp. 189-190. 



