196 MUCOUS MEMBEA^ES 



lines, but many forms will be found which might well be placed 

 under either of two or more types. Hence any classification of 

 secreting glands becomes more or less arbitrary ; nevertheless such 

 a classification is of extreme importance as serving to establish in 

 the mind of the student certain typical pictures with which indi- 

 vidual glands may be compared, and important structural details 

 will thus be noticed which might otherwise escape observation. 



