404 



HISTOLOGY 



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 11 



a huge quantity of granular material which destroys the distal part of 

 their cytoplasm and fills the entire lumen solidly with the secretion. 



This secretion is the offen- 

 sive matter. The proximal 

 parts of the cells remain un- 

 ?&*<& differentiated, and form a 



lining of cytoplasm in 

 which the flattened nuclei 

 lie. 



Outside of the nuclear 

 layer appears a single, close- 

 set layer of smooth muscle 

 cells, two of which are 

 shown in oblique section in 

 Figure 366. They serve to 

 contract the gland when the 

 secretion is to be discharged. 

 Covering the muscle layer 

 is a light connective tissue 

 which contains, between its 

 thin outer and inner plates, 

 a plexus of capillaries. Still 

 outside of this is a septum 

 of connective tissue which 

 lies between all of these 

 closely placed glands. A 

 duct is present, in a more specialized form than in the neighboring 

 mucous glands. It has a complicated set of muscles for controlling the 

 discharge of the secretion. When the gland is discharged, its lining is 

 destroyed and renewed by the growth of a bud from the side, as has 

 been described by Esterly and others. 



The secretion, when discharged, is a modified mucus, and is watery 

 instead of oily, as in the preceding vertebrate forms. The organs have 

 been considered as offensively odorous rather than poisonous, because 

 the animal has no means of injecting the secretion into the blood of an 

 enemy or victim. 



Vastly different from any of the above are the various tissues found in 

 invertebrate animals, and which are used to produce either attractive or 

 repulsive odors. We naturally understand those found in the air- 

 breathing animals best. There are undoubtedly many such organs to 

 be found in the water-breathing animals that we do not know of and 

 may never find. 



It is among the insects that the greatest number and variety of odorous 



FIG. 366. Part of the wall of a repugnatorial gland 

 from the skin of a toad, Bufo. sec.c., secreting cells; 

 sec.g., granular secretion; mus.c., parts of two of the 

 investing smooth muscle cells; bl.l., connective-tissue 

 layer containing the blood supply in capillaries; 

 conn.t., connective- tissue septum belonging to the 

 corium and found between all the glands. X 1000. 



