SECRETION. 349 



Great variety is observable both in the form and 

 structure of different glands, and in the mode in 

 which their blood-vessels are distributed. In 

 animals which are furnished with an extensive 

 circulation, 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 par- 

 ticular 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, like the fibres of a camel- 

 hair pencil : this is called the peuicillated struc- 

 ture. Sometimes the minute branches, instead 

 of proceeding parallel to each other after their 

 division, separate like rays from a centre, pre- 

 senting a stellated, or star-like arrangement. In 

 the greater number of instances, the smaller 

 arteries take a tortuous course, and are some- 

 times coiled into spirals, but generally the con- 

 volutions are too intricate to admit of being 

 unravelled. It is only by the aid of the micros- 

 cope that these minute and delicate structures 

 can be rendered visible ; but the fallacy, to 

 which all observations requiring the application 

 of high magnifying powers are liable, is a serious 



intestiiuil canal of the Gryllotalpa, or aiolc-cricket. Phil. Tran. 

 for 1825, p. 227. 



