DEVELOPMENT OF CONNECTIVE TISSUE. 241 



tissues and the vessels are esentially different from those which produce the other 

 tissues, and that they have wandered in between the other cells of the mesoblast 

 from the peripheral part of the blastoderm (parablast-cells of His, mesenchyme cells 

 of Hertwig. See Embryology, pp. 25-27). 



The mesoblast cells which are concerned in the formation of the connective 

 tissues are at first rounded in shape, and loosely packed, and exhibit amoeboid 

 movements when examined on the warm stage. Subsequently they become 

 irregularly ramified and tend to unite with one another so as to form a kind of cell- 

 network with open interstices. These interstices are at first occupied by an albu- 

 minous fluid which later acquires a mucous or muco-albuminous character and 

 becomes more consistent : it may now be spoken of as the ground-substance or 

 matrix. 



In this ground-substance fibres become developed of the two kinds, white and 

 elastic, but the manner in which they are formed is by no means clear ; and two 

 distinct and opposed views are held by histologists upon the subject. According to 

 the one view, the bundles of white fibrils are produced by a direct conversion 

 of the protoplasm of some of the cells, the others remaining as the permanent con- 

 nective tissue corpuscles ; or the permanent corpuscles represent embryonic cells, 

 layers of whose protoplasm have been successively converted into fibrillar tissue, the 

 cells, meanwhile, after each such conversion, growing again to their original size, 



Fig. 282. DEVELOPMENT OF ELASTIC TISSUE 



BY DEPOSITION OF FINK GRANULES. 



(Ranvier, ) 



g, moniliform fibres formed of rows of 

 "elastin " granules ; p, flat platelike expan- 

 sion of elastic substance formed by the fusion 

 of " elastin " granules. f 



and at length remaining in contact 

 with the bundle of fibres which 

 they have assisted to form. Simi- 

 larly the elastic fibres are believed 

 to be formed of the processes of 

 some others of the embryonic cells, 

 which become connected with pro- 

 cesses of neighbouring cells, and undergoing a chemical transformation, produce the 

 networks of elastic fibres. According to the other view the fibres, both white and 

 elastic, are formed by a deposit in the intercellular substance, and not by a direct 

 change of the protoplasm of the cells, with which indeed they are not connected ; 

 although it is not excluded that the deposition may in some way or other be 

 influenced, or even caused by the pre-existing cells. 



In favour of the former view is the fact that in young connective tissue there are 

 sometimes to be seen long cells with fibrillated protoplasm which might be regarded 

 as in process of conversion into bundles of white fibrils. And various authors have 

 described an apparent continuity both in young and in developed connective tissue of 

 the elastic fibres with the cells of the tissue, or even with their nuclei. 



In favour of the latter view may be instanced the appearance of the jelly-like 

 connective tissue of the early embryo in which the fibres of both kinds can be seen 

 coursing through the jelly-like intercellular substance, apart entirely from the cells. 

 In the case of the elastic fibres, these, as shown by Ranvier, appear in the form of 

 rows of granules or globules, which subsequently become fused together end to end, 

 and are not at any time continuous with cells (fig. 282). To form an elastic mem- 

 brane, in place of being arranged in lines the globules are deposited in small patches. 



