398 
E. RAY LANKESTER. 
well-stained specimens of Amphioxus we find that the nuclei of 
the cells which give rise to these varieties of skeletal substance 
are always arranged in simple layers, in fact are epithelial in 
character, and, as Hatschek (16) has recently shown, are in fact 
the epithelia bounding the primitive myocoel pouches or their 
outgrowths, as explained above (see PI. XXXYI A, figs. 6, 7, 
copied from Hatschek). 
Beneath the epidermis we find a dense lamina supporting the 
epithelial cells ; beneath this, again, a softer, less dense gela- 
tinous substance, and more deeply a second very delicate lamina, 
on which we find the connective-tissue cells. These four 
laminae constitute the cutis. The cells of the deepest layer 
are the only cells of the connective tissue (see PI. XXXYI A, 
fig. 1), and must be regarded as the matrix-cells of the various 
layers of skeletal substance superficial to them. 
In the expanded regions of the median fin at the two 
extremities of the body the substance of the fin is formed by 
the gelatinous tissue, which is excavated by small irregular 
canals and spaces clothed with the epithelial connective-tissue 
cells. Thus a cartilaginoid tissue is produced, no longer a 
plane lamelliform deposit, but a tissue which increases in three 
dimensions (see Pouchet, this Journal, vol. xx, p. 421). 
The thickened mass of cutis bounding the outer wall of the 
metapleural canal is formed by an increase in the gelatinous 
layer, which not only is thickened but contains numerous 
fibrillse. 
The fin-rays consist of a fibro-gelatinous substance, which is 
invested by an epithelial layer. The fin-ray boxes or compart- 
ments are, according to the important observations of Hatschek, 
survivals of the myoccelomic pouches, and are, at one time (as 
they are permanently at the extremities of the series) simple 
cavities lined with the myoccelomic epithelium. In the floor 
of the cavity beneath the epithelium the fibro-gelatinous fin- 
ray is formed, and gradually grows up into the compartment 
clothed with the epithelium. There are no canalicular spaces 
in the fin-ray, and no cells sunk in its substance. 
The skeletal tissue which surrounds the notochord and 
