SECRETION. 313 



Structure of different glands, and in the mode in 

 which their blood-vessels are distributed. In ani- 

 mals which are furnished with an extensive circu- 

 lation, the vessels supplying the glands with blood 

 are distributed in various modes ; and it is evident 

 that each plan has been designedly selected with 

 reference to the nature of the particular secretion 

 to be performed, although we are here unable to 

 follow the connexion between the means and the 

 end. In some glands, for example, the minute 

 arteries, on their arrival at the organ, suddenly 

 divide into a great number of smaller branches, 

 hke the fibres of a camel-hair pencil : this is called 

 the penicillated structure. Sometimes the minute 

 branches, instead of proceeding parallel to each 

 other after their division, separate like rays from a 

 centre, presenting a stellated, or star-like arrange- 

 ment. In the greater number of instances, the 

 smaller arteries take a tortuous course, and are 

 sometimes coiled into spirals, but generally the 

 convolutions are too intricate to admit of being 

 unravelled. It is only by the aid of the microscope 

 that these minute and delicate structures can be 

 rendered visible ; but the fallacy, to which all ob- 

 servations requiring the application of high magni- 

 fying powers are liable, is a serious obstacle to the 

 advancement of our knowledge in this department 

 of physiology. Almost the only result, therefore, 

 which can be collected from these laborious re- 

 searches in microscopic anatomy, is that nature 

 has employed a great diversity of means for the 

 accomplishment of secretion ; but we still remain 

 in ignorance as to the kind of adaptation, which 

 must assuredly exist, of each structure to its respec- 



