8 VASCULOGENESIS IN THE CAT 



be first studied by the method of injection, we should have a his- 

 tory of the ureteric bud from the standpoint of its lumen. It 

 would have sprouted, giving branches of many orders, and by 

 growth in continuity its arborizations would in time form their 

 definitive terminals, the Bowman's capsules. Should an inves- 

 tigator, with a belated confidence in slides and reconstruction, 

 have ventured to observe the renal vesicles, he might have been 

 told he had been misled by artifacts. Had he objected that they 

 were constant, had definite structural characters, and were local- 

 ized with exquisite precision, he might at length have obtained 

 their tardy recognition. But it is probable, for doctrines as well 

 as masses have momentum and inertia, that he would then have 

 been informed, that his vesicles were but separated sprouts, be- 

 cause neplii'othelium comes only from nephrothelium. And 

 these arguments would be as justifiable, nay as necessary, in the 

 one case as in the other, if ultimate reliance is placed on the in- 

 jection method which can only reveal continuity of lumina. The 

 logic is good, the argument the typical scholastic deduction of the 

 special case from the general principle, but the principle is intu- 

 itive and arbitrary, not inductive. 



The blind terminals of vessels in the mammalian foetus are a 

 favorite topic for study by injection, but so far as I am aware, 

 the possibility of their regressive nature has never been seriously 

 considered; it has simply been assumed that they were always 

 growing sprouts. I desire here rather to note the gap in the evi- 

 dence than to question this mode of growth as a factor in the ex- 

 tension of formed \'essels in late embryonic stages and in tlie foetus. 



W. G. MacCallum^ ('02) made a careful and excellent histo- 

 logical study of lymphatic terminals in the skin of pig foetuses, 

 from 6 cm. to 15 cm. in length, and reached the conclusion that 

 the lymphatics did not communicate with tissue spaces. From 

 their extremities pi'oject strands of cells in a single or double row 

 which rim for some distance in the embryonal connective tissue, 

 or join another lymphatic. He thought that few of these cells 

 were in syncytial relation with adjacent fibroblasts.' Into the 



2 1902. Arch. f. Anat. u. Entwickelungsgesch., p. 273. 



' Expont'iits of the doctrine of specificity seem inclined to lay stress on this 

 point as indicating the independence of endothelium. In view of the interdermal 



