368 TTTE EVOLUTION OF MAN. 



the most recent group of tissues, that which originated last. 

 Under this name are included those epithelial-like tissues 

 which line the closed inner cavities of the body (the ccelom, 

 chest-cavity, ventral cavity, heart-cavity, blood-vessels, etc 

 (Fig. 296). In addition to this vascular carpet (endo- 

 theliuin), the liquids containing cells, which fill these 

 cavities (lymph, blood, serum, etc.), must be classed with 

 this tissue (Fig. 297)- All these tissues may be grouped as 

 vasalia. His wrongly ascribed to them a quite different, 

 " parablastic " origin (from the nutritive yelk); they are, 

 however, products of the intestinal-fibrous layer (and partly, 

 perhaps, of the skin-fibrous layer). As the co3loma and the 

 whole vascular system is of more recent phylogenetic origin, 

 its peculiar tissues must also be more recent. 



This phylogenetic explanation of the ontogenetic suc- 

 cession of the tissues and of the organ systems arising from 

 them, appears to me to be satisfactorily proved by Com- 

 parative Anatomy, and by the Gastrsea theory. If it is 

 correct, it discloses an interesting glimpse into the entirely 

 various age of the most important constituent parts of our 

 body. The human skin and intestine are, according to this, 

 many thousands of years older than the muscles and nerves; 

 these again are much more ancient than kidneys and blood- 

 vQgsels, and the latter, finally, are many thousands of years 

 older than the skeleton and the sexual organs. The com- 

 mon view, that the vascular system is one of the most 

 important and original organ-systems, is, therefore, erro- 

 neous ; it is as false as the assumption of Aristotle that 

 the heart is the first part to form in the incubated chick. 

 On the contrary, all lower Intestinal Animals show plainly 

 that the historic evolution of the vascular system did not 



