7S 



OENERAL PRINCIPLES OF ZOOLOGY. 



acii^ous belong the salivary glands, not only of the vertebrates, but 

 also of the arthropods and niollusos. 



Fig. 30.— Tubular glands. (After Toldt.) ^1, glands of Liebei-kiihn from the human 

 intestine; A', of the conjunctiva of the eye; U, of the cat's stomach; C, from the 

 medullary pyramids of the dog's kidney; X>, from the cortex of tlie rabbit's 

 kidney. 



Sexual Epithelium. — The sexual cells may be considered in 

 connexion "ndth glandular epithelium. As the secretion of some 



f 





Fio. 31.— Acinous salivary gland of tlie a|)hid nythrzin valaiihmfta. (After List ) In 

 some acini the nuclei and boundaries of the cells are shown. 



glands must be expelled fronr the body, so the sexual cells are 

 elements which differ from the rest of the organism, and must 

 reach tlio exterior in order to perform tlieir function. Just as the 



