106 THE ANATOMY OF THE HONEY BEE. 



The Malpighian tubules are regarded as excretory in function and 

 are supposed to remove from the 'blood the nitrogenous waste prod- 

 ucts resulting from metabolism. Minute crystals of urates are often 

 to be found in them and they probably perform the work of the 

 kidneys in vertebrate animals. 



The large intestine (fig. 42, Red), called the rectum in insects, is 

 an enormous sac which may lie limp and flabby in the rear part 

 of the body or it may be so immensely distended by the amount of 

 its solid and liquid contents as to occupy a large part of the abdomi- 

 nal cavity. The recognizable elements of the material within it 

 consist mostly of the empty shells of pollen grains or of grains hav- 

 ing their contents greatly shrunken and distorted — presumably as 

 a result of the absorption of the protoplasm, although a considerable 

 number are usually present which are only slightly digested, while 

 there are always to be observed a few perfect and fresh-looking 

 grains showing no evidence at all of digestion. The rest of the in- 

 definite mass of solid rectal material consists of some unrecognizable, 

 finely triturated substance, probably derived in part from fragments 

 of the peritrophic membranes. There are always present a few bits 

 of feathered bee hairs. 



The epithelium of the rectum is, like that of the CESophagus, rudi- 

 mentary, being distinguishable only by the nuclei (fig. 46 F, Nu) 

 remaining in the outer layer of the thick transparent intima {Int). 

 Outside of this is an external layer of longitudinal muscle fibers 

 {LMcl) and an inner layer of transverse fibers {TMcT). The intima 

 (/wi) is thrown into numerous folds whose edges qonverge, forming 

 pocketlike grooves between them in which are lodged small masses 

 of the rectal contents. This is very suggestive that absorption takes 

 place in this part of the alimentary tract, although it is not com- 

 monly supposed to do so, but if the pollen is not fully digested until 

 it reaches the rectum, how can it be absorbed by the anterior part 

 of the alimentary canal? 



The so-called rectal glands (fig. 42, RGT) consist of six hollow 

 epithelial tubes (fig. 46 F, RGl) and are the only parts of the rectal 

 epithelium in which the cells are well developed. The cells on the 

 outside of each " gland " are small, but the inner ones are very large 

 and are covered by a thick layer of dark chitin {Int). The lumen 

 is intercellular and does not communicate with that of the rectum. 

 "WTien the rectum is distended the " glands " bulge out on the surface 

 as six short opaque ridges (fig. 42, RGl) , but when it is empty they 

 sink into the walls as in figure 46 F. Nothing is known of the 

 function of these organs, and their glandular nature is entirely con- 

 jectural. If they are glands, it is not clear why the intima should 

 be so especially dense on their inner faces. 



