FUNCTIONS OF DUCTLESS GLANDS. 329 



from the vessels into the sacculi, arid gradually develop into 

 nuclei or cytoblasts, which may be further developed into cells ; 

 that in the growth of these nuclei and cells, the materials de- 



FIG. 108. 



The figure shows a portion of a small artery, to one of the twigs of which the 

 Malpighian corpuscles are attached. 



rived from the blood are elaborated into a higher condition of 

 organization ; and that when liberated by the dissolution of 

 these cells, they pass into the lymphatics, or are again received 

 into the blood, whose aptness for nutrition they contribute to 

 maintain. 



The opinion that the vascular glands thus serve for the 

 higher organization of the blood, is supported by their being 

 all especially active in the discharge of their functions during 

 foetal life and childhood, when, for the development and 

 growth of the body, the most abundant supply of highly or- 

 ganized blood is necessary. The bulk of the thymus gland, in 

 proportion to that of the body, appears to bear almost a direct 

 proportion to the activity of the body's development and 

 growth, and when, at the period of puberty, the development 

 of the body may be said to be complete,*the gland wastes, and 

 finally disappears. The thyroid gland and supra-renal cap- 

 sules, also, though they probably never cease to discharge some 



