1HK ORGANS OF Till: P \IK LATH ll ME8ENCHYMK 



\\ iv by embracing these organs in a chapter by themselves and 



lisfuiM.u r tin-in uj-an lV..m tlio organs of the i: : Idle, and 



miter irt rin la\ 



It i> tii. original province of the intermediate layer to form a 



packing :ind >ust-ntative substance between tl pithelial layers, a 



fact which stands out with the greatest di-tim-i ness parti.-ulai 

 the lower groups, as for example in tin- < '< -Inn. -rate-. I* there- 

 fore closely dependent upon tin- epithelial the. matter 

 distribution. When the p-rm-layrr- are rai-.-d up into folds, it 

 s between the layers of the fold as a sustentative lamella : 

 \\hen the L r erm -layers are folded inv. ves the parts 

 an being differentiated -as for exam] <brates, then*- 

 t uhe, the masses of tin- t ra ; ripsd mu--l-s, the secretory 

 I arenchyma of glands, the optic cups, and the auditory vesicles 

 and pru\ides them with a special envelopment that adjusts i 

 to them (the membranes of the brain, the perimy>ium, and the 

 connective-tissue substance of the glands). In consequence of this 

 the intermediate layer, in the same proportion as the germ-layers 

 become more fully organic -d. becomes itself con\ ' 

 ordinarily complicated framework, and resolvt d into thf n.. 

 gent organs, by the formation of evaginations and imaginations 

 and the con>trieting off of pan-. 



The form of the intnim dial*- layrr thus pr< duo d is of a second- 

 ary nature, for it is d. p< L-! inorphosis of the germ- 

 layers, with which it is most intimately connected. But in addi 1 

 the intermediate layer, owing to its own great power of metamor- 

 phosis, acquires in all higher organisms, particularly in the Verte- 

 brates, an intricate stnu-tm-.-. >pecially in the way of histological 

 nnorphosis. In this way it gives rise to a 



lon^: various organs the cartilaginous and bony skeletal 



parts, tl ses, and tendons, the blood-vessels and 



lymphatic ifhi 



It is therefor- lining to t nter here somewhat more particularly 

 upon a di<cu*>ii>n of the /<////'//>& of histological d 



ially to incniin- in what manner it is concerned in the origin of 

 organs differentiated in the mes ; 



The most primitive and >implt-t form of mesenchyme isgelatii 

 t isMie. Not only does it predominate in the lower grou; mals, 



but it is also the first to be developed in all Vertebrates, out of the em- 

 bryonic cells of the interiiieu '*re the forerunner and 

 the foundation of all the remaining forms of sustentative substance- 



