604 ORGANS OF SECRETION. 



rature of their body and their great muscular activity, are 

 formed, expended, and reproduced with comparative rapidity, 

 the mucous secretions of their buccal, nasal, and intestinal 

 cavities, the serous transudations into shut cavities, as the 

 abdomen and the pericardium, and especially the oily syno- 

 vial secretions into the capsules of their ever-active joints. 

 The fluids of the eye, the ear, the lachrymal, the Harderian, 

 and the nasal glands, the cesophageal, ingluvial, and gastric 

 or proventricular glands, and the secretions of the oviducts, 

 are all rapidly expended and reproduced in this most active 

 and hot-blooded of all the vertebrated classes. This condi- 

 tion of the secreted fluids of birds is not dependant on a 

 more highly developed or complicated structure of their 

 glands, which are still comparatively simple, but rather on 

 the rapid transmission of highly arterialized and heated blood 

 through their texture, and the high development of the 

 nervous system on which the secretions so immediately 

 depend. 



The secreting organs have mostly arrived at their greatest 

 complexness in the mammiferous tribes, as indicated by the 

 number and minuteness of their ultimate tubuli, their sepa- 

 ration from the surface from which they originate by the 

 elongation and concentration of their ducts, by the formation 

 of reservoirs to retain and accumulate the secretions, and 

 by the size and vascularity of the entire glandular masses. 

 The plan of development, however, in every gland, appears 

 to be the same as in lower classes, commencing by simple 

 follicular protrusions from the formative surface, which acquire 

 thickened vascular parietes, forming a blastema, for the 

 further production of coeca and ramified tubuli, to compose 

 the lobules and lobes of the gland, and thus to increase the 

 extent of surface over which the capillary blood vessels are 

 spread to afford the materials of the secretion. The salivary 

 glands commence from the mucous membrane of the mouth 

 as simple follicles, these bud out from their periphery further 

 follicles and ramified tubuli, which extend through the soft 

 vascular and lobulated blastema, the closed ends of the tubuli 

 forming small vesicular enlargements, and the blastema gra- 

 dually disappearing as its space becomes occupied with the 

 developing secerning tubes. The blastema early assumes a 

 lobulated exterior form, corresponding with the future lobed 



