136 PROFESSOR E. KAY LANKESTER. 



and enclosing in their reticulations groups of cells embedded 

 in matrix (PI. IX, fig. 1) . This structure very closely resembles 

 that of Vertebrate elastic fibro-cartilage. 



The chief diflference between this tissue and typical Verte- 

 brate cartilage, so far as form is concerned (apart from 

 chemical constitution) is in the mode of multiplication of the 

 embedded cells. The cells are, it is true, just as in Vertebrate 

 typical cartilage, embedded in a firm structureless matrix, 

 which fits closely to the periphery of the cell protoplasm, being 

 only distinguishable therefrom by the slight difi'erence of the 

 refractive indices of the two substances. But it is characteristic 

 of the present tissue for its cells to multiply linearly, that 

 is by growth along and division across one axis : rarely only 

 do they multiply along an axis at right angles to this. The 

 tissue is in fact essentially fibrous (monaxial cell division) or 

 rarely membranous (biaxial). At the same time the cells 

 resulting from the division of parent cells remain in closely 

 adherent groups (either rows or irregular masses) as shown in 

 PI. VII., and only here and there do we find isolated cells 

 entirely surrounded by matrix. This implies that the activity of 

 such cells in producing matrix around themselves is not great, 

 or at any rate, not uniformly present. In contrast to this we 

 find that a cell of Vertebrate cartilage no sooner takes its origin 

 by division from a parent cell than it becomes separated from 

 that parent by a layer of matrix (capsule) which rapidly increases 

 in volume. Every cell appears to be thus constantly active in 

 developing matrix and becomes separated from its parent cell 

 by a considerable interval. At the same time all the cells of 

 a tract of Vertebrate cartilage are approximately equally 

 active in division, and all may be rapidly growing and multi- 

 plying by division or all may be comparatively quiescent. This 

 equality and isolation of the cells of typical Vertebrate 

 cartilage is accompanied by another feature in growth in which 

 it difi'crs I think constantly from all but the deepest parts of 

 the tissue which forms the tendinous entosternite of Limulus. 

 Vertebrate cartilage (excepting the white fibro-cartilage which 

 is transitional in its characters between tendon and typical 



