584 Transactions of the Soaietij. 



Fig. 7. — A similar condition, where the junction of two cells a and d and their 

 vacuoles forming one cavity is very plainly marked by silver lines. The dotted 

 line represents the continuation of the silver marking on tlie lower surface of 

 the tube formed. A third cell c has placed itself, according to rule, against the 

 joint formed by a and d, but communication has not yet been effected with the 

 lumen of the capillary. 



Fig. 8. — Shows the formation of a capillary plexus. The vacuoles in a and d, 

 having formed one cavity, are about to establish a communication with the blood- 

 vessel 6. Three cells by their processes are forming a junction at g. Cell e is 

 stretching out a process to form a communication with a wandering cell /, which 

 has not yet begun to elongate its protoplasm. 



Fig. 9 shows a junction being formed at an acute angle by cells a and d, so 

 as to construct a loop between two capillary loops, but only cell d has vacuolated, 

 and it has not yet connected its cavity with the circulation. 



Fig. 10. — A similar loop between two capillary loops g and h, being formed by 

 three cells a, b, and c, none of which has as yet begun to vacuolate. 



Fig. 11. — A branch capillary developing in accordance with the plan seen 

 in the preceding figures, cell a having vacuolated, and the vacuole being about to 

 become connected with the lumen of the blood-vessel 6. This figure is to be 

 compared with Fig. 1(3, which apparently represents retrogression, both figures 

 being taken from the same field of the Microscope in a preparation of the omentum 

 of a newly born kitten. 



Fig. 12 represents the formation of a largo capillary loop or plexus. At A 

 the whole plan has been drawn under a low power of 100 diameters, while the 

 special points of interest have again been drawn at tlie same high power as the 

 rest of the drawings. The nodal points in the existing capillaries to be connected 

 are formed at a and at h and c, wliile c, f, g, and h represent some of the links on 

 the future chain. Of these links, g is formed of tliree cells joined togetlier in the 

 usual plan, and of these, g and g' are vacuolating ; a nucleus-like body, resembling 

 also a blood-corpuscle seen edgeways, appears to float free in the vacuole of g. 



Fig. 13 shows development and retrogression of vessels going on at the same 

 moment and in the same field of the Microscope, owing to changes in the circula- 

 Intion at birth, a a', terminations of a retrograding vessel still connected with the 

 circulation ; b b' portions of tlie blood-vessel formerly continuous from a to a' and 

 still containing tlie blond-corpuscles e e, which remained in them at the moment of 

 separation ; c newly developed vessel with three branches d, d', d'', in course of 

 development ; //, nuclei of the cells of the wall of the capillary. 



Fig. 14 shows a developing loop a becoming connected with the circulation at 

 b b', the component cells of which follow the rules already noticed. 



Fig. 15 shows retrogression of blood-vessels in old age, and failure to 

 assimilate food, which was plentiful. The loop a is about to break off from the 

 circulation at 6 6', being exactly the converse of Fig. 14; blood-corpuscles at ee; 

 nuclei of the cells forming capillary wall at //. 



Fig. 16. — A drawing under higher power of 6' Fig. 13, representing a so-called 

 vasoformative cell, but in reality a portion of a retrograding blood-vessel. 

 Compare with developing capillary in Fig. 11, from the same preparation. 



Fig. 17. — A small portion of a long capillary loop in retrogression (from a rat 

 which had evidently died of starvation), being the portion still attached to the 

 plexus, but shut to the circulation, e e, blood-corpuscles ; //, nuclei of cell wall. 



Fig. 18. — A similar portion of retrograding capillary, collapsed throughout, and 

 undergoing absorption. It is about to break up into its constituent cells a a. From 

 the same preparation as Fig. 17. 



Fig. 19, from the same animal as Fig. 15, shows a portion of retrograding 

 capillary from which one cell a is about to separate itself. That cell contains two 

 blood-corpuscles 6, nearly absorbed, c, granular matter of the nature of fat or of blood- 

 pigment ; dd, other blood-corpuscles still normal ; e e, nuclei of wall of capillary. 



Fig. 13 is drawn to a scale of 170 diameters ; Figs. 17 and 18 to 280 diameters ; all 

 the others under the same power of 330 diameters, by the aid of the camera lucida. 



