Development, dte., of Blood-vessels. By G. and F, E. Hoggan. 571 



that portions of capillaries show the junction markings of the 

 hollow cells composing them, before ever they have become con- 

 nected with the circulation. 



We have found that a new development of blood-vessels takes 

 place solely by the aid and addition of the wandering cells.* In 

 the membranous sheet under consideration, the only cells present, 

 apart from the layers of endothelium covering the two surfaces of 

 the rapidly growing tissue, are the wandering cells. They may be 

 seen here in at least three conditions. They may be found 

 wandering purposeless over the free surface of either layer of endo- 

 thelium, or through the soft gelatinous matrix forming the mem- 

 brane between these layers. If the tissue has been properly 

 prepared, they are generally found branched in the latter locality, 

 although on the free surfaces they have retracted into a globular or 

 circular form, being surrounded by no matrix to retain them in the 

 branched condition when the silver is applied to fix them. If the 

 animal has been injected and left to cool before it is opened, and the 

 silver solution be then applied, they will probably appear round in 

 shape within the matrix, and very plentiful on the free surfaces in 

 the same form ; or they may be found developing into fat-cells in the 

 neighbourhood of the blood-vessels, in which condition they may 

 either appear round or with matiij branches, according to the condi- 

 tions of preparation already referred to. They may have more than 

 one nucleus in the purely wandering condition, but they have not 

 more than one nucleus as a rule when developing into a fat-cell. 

 Again, they may be found placing or having placed themselves in 

 position to form or to strengthen a blood-vessel in course of deve- 

 lopment. The methodical manner in which this is effected would 

 almost argue an instinct or intelligence worthy of higher animals ; and 

 although the directions the cells move in when forming the new 

 vessel may be manifold, they seem to follow a regular course 

 throughout. They may either plant themselves at a point in a 

 blood-vessel where a connection is to be formed, and prolong their 

 protoplasmic cell substance to join hands with another cell liuk in 

 the chain of capillary development, as at a, Fig. 9 (Plate XV.), and 

 e, Fig. 8, or, as is more common, they may appear external to the 

 future point of junction, and, stretching towards it their proto- 

 plasmic arm, thus complete the connection. This peripheral position 

 may be either in direct linear continuation of a new vessel, as at d, 



• Wc tliink it unnecessary that we should aguin enter at any lengtli into the 

 rcasims we have jdready piven in our furnior nrtiolu on tlic Fut-cell, for rejecting 

 tlic liypotliesis that tlio fixctl cc-\U of the connective tinsue have any Bliare in tlio 

 fornialion of blood-vo8.s. Is, fat-cclLs, &c. We cannot admit tiiat any fixed cell of 

 any tis.sue can normally devcloj) directly into the fixed cell of any other tissue. 

 A "ciinecr cell may indeed impress its charact<r u|ion any lixed or ond)ryonic cells 

 near it, so that these also Income cancer cells; hut, normally, fixed cells can only 

 arise from or return to emhryouic cells. 



