242 



DEVELOPMENT OF CONNECTIVE TISSUE. 



and by their fusion the membrane is formed (p). In elastic cartilage the granules 

 first make their appearance, it is true, in the immediate neighbourhood of the 

 cartilage-cells ; but although this renders it probable that the deposition of the 

 granules -is influenced by the cells, it does not prove that they are formed by a 

 direct conversion of the cell-protoplasm. Indeed, the subsequent extension of the 

 fibres into those parts of the matrix Avhich were previously clear of them (a process 

 which can be easily followed in the arytenoid cartilage of the calf), and in which no 

 such direct conversion of cell protoplasm seems possible, is a strong argument in 

 favour of the deposition hypothesis. 



The view which supposes that a direct conversion of the protoplasm of the connective 

 tissue cells takes place into fibres, both white and elastic, has of late years been widely 

 adopted, but it seems to rest largely upon a desire to interpret the facts in accordance with 

 the conception (originally formulated by Beale and M. Schultze), according to which every 

 part of an organised body consists either of protoplasm (formative matter), or of material 

 which has been protoplasm (formed material) ; the idea of a deposition or change occurring 

 outside the cells in the intercellular substance being excluded. It is, however, not difficult to 

 show that a formation of fibres may occur in the animal organism without a direct transfor- 

 mation of protoplasm, although the materials for such formation may be furnished by cells. 

 Thus in those coelenterates in which a low form of connective tissue first makes its appearance, 

 this is distinguished by a total absence of cellular elements, a ground-substance only being 

 developed and fibres becoming formed in it. Again, the fibres of the shell-membrane of the 

 bird's egg are certainly not formed by the direct conversion of the protoplasm of the cells 

 which line the oviduct, although they are formed in matter secreted by those cells, and 

 it is through their agency that the deposit occurs in a fibrous form. 



In the formation of retiform tissue the ground-substance appears to become 

 entirely liquefied except where it enters into the composition of the reticulum, and 

 the cells of the tissue become applied to the anastomosing fibril bundles, and by 

 their union constitute a network of branched cells enveloping the network of fibrils. 



Fig. 283. JELLY OF WHARTON. (Ranvier.) 



r, ramified cells intercommunicating by their branches ; I, a row of leucocytes or migratory cells ; 

 /, /, fibres coursing through the ground-substance. 



In lymphoid tissue the meshes become occupied by lymph corpuscles which may 

 originally have come from the blood or lymphatic vessels, but afterwards multiply 

 by cell-division. 



The jelly-like connective tissue of the early embryo persists in the umbilical 

 cord until birth as the so-called jelly of Wharton (fig. 283). Elsewhere it has largely 

 lost its jelly-like character in consequence of the development of fibres in the 

 ground-substance, but the amount to which they are developed varies greatly in 



