Development, dc, of Blood-vessels. By G. and F. E. Eoggan. 583 



cient nutrition or assimilation of food, on the one hand, or to 

 changes in the development of an animal, on the other, the only 

 peculiarity being that while in the latter case development and 

 retrogression go on simultaneously and side by side, in the two 

 former cases only retrogression goes on at one time, there being no 

 room or reason for development, just as during development of blood- 

 vessels in the adult there can be no retrogression at the same time. 



Bearing in mind, therefore, the small bodies sometimes seen in 

 vacuolating cells during the formation of blood-vessels, as in Fig 3, 

 these bodies being in general too small to be mistaken for blood- 

 corpuscles, we have come to the conclusion that the vasoformative 

 cells are neither cells nor cavities, but are only intercepted portions 

 of a retrograding capillary or larger vessel, as the case may be, 

 and still containing the blood-corpuscles which lay within the vessel 

 before it broke up into fragments. 



The results of this research may be summarized in very few 

 words. When new blood-vessels are necessary, the wandering cells 

 come and plant themselves in position according to a definite plan ; 

 through these, when hollowed out, the circulation of the blood is 

 established or permitted. When the blood-vessels of any part are 

 no longer necessary, they break up into their individual cells, and 

 these separated links of the broken-up chain move off in their 

 original condition of wandering cells. A simple cycle of life, or 

 functional phase ; much simpler, indeed, than the cycle we have 

 described in the life of the fat-cell (a companion study already pub- 

 lished in this Journal), but none the less evident because it is simple. 



EXPLANATION OF PLATE XV. 



(Drawings and preparations by the authors.) 



The first fourteen figures illustrate the development of blood-vessels, and 

 Figures 13 and 15 to 19 illustrate their retrogre.ssiun. Figures 11, 13, and IG are 

 from the omentum of the newly born kitten ; Figures 15, 17, and 18 are frum the 

 broad ligament of the r.it ; the re;<t are from the broud ligament of pregnant mice. 

 They have all been stained by silver and pyrogallate of iron, and mounted in 

 glycerine. 



Fig. 1 shows a wandering cell a forming a junction with a blood-vessel 6, 

 whicli, as if in sympathy, has dimpled or bulged its wall towards the new comer. 



Fig. 2. — A similar cell «, in like relationship to a capillary 6, but in a stage 

 further advanced than Fig. 1. In this case the capillary has bent its whole tube 

 in sympathy. A second cell c has placed itself against the joint as if to 

 Btiengthen it. 



Fig. 3. — A still further advanced condition, in which a second cell-link <i has 

 been added to a ; a, moreover, is vacuolating, and shows four small globular IxKiics 

 within the vacunle. An earlier stage of vacunlution is seen in Fig. 12, at c and i'. 



Fig. 4. — A still further advanced coudition, in which cells a and rare vacui'lat- 

 ing respectively towards'', the proximal, and </, the distal communication. 



Fig. 5. — A similar ctmdition where vacuolalion has been going on in cells <i 

 and d before connection is established with the capillary '>. 



Fig. G. — A similar condition where the vacuoles in two ct ll.s a and (/ have 

 joined to form one cavity before forming a communication with a tliinl cell, 

 vacuole h intervening between tlieni and the capillary. Th ■ i.s. ijated cell / 1<> the 

 right of Fig. 1 belongs to this figure. [Fio. 7 



