140 THE ORIGIN OF VERTEBRATES 
the entapophysial ligament, on the contrary, just like muco-cartilage, 
takes on an intense purple colour when stained with thionin. It 
possesses a mucoid substratum, just as does muco-cartilage, and in 
both cases a perfectly similar soft cartilage is born from it. 
One difference, however, exists between the branchial cartilages of 
these two animals; the innermost axial layer of the branchial bar of 
M@ 3 
PROSOMA 
Fiag.'59,—Driacram oF LImULvs, To sHow THE NERVES TO THE APPENDAGES (1-13) 
AND THE BRANCHIAL CARTILAGES, 
The branchial cartilages and the entapophysial ligaments are coloured blue, the 
branchie red. gl., generative and hepatic glands surrounding the central nervous 
system and passing into the base of the flabellum (/72.). 
Limulus is very apt to contain a specially hard substance, apparently 
chalky in nature, so that it breaks up in sections, and gives the 
appearance of a broken-down spongy mass; if, however, the tissue is 
first placed in a solution of hydrochloric acid, it then cuts easily, and 
the whole tissue is seen to be of the same structure throughout, the 
main difference being that the capsular spaces in the axial region 
are much larger and much more free from cell-protoplasm than are 
those of the smaller younger cells near the periphery. 
