AMPHIOXUS LANCEOLATUS. 
399 
forms the intermuscular septa and neural sheath, is, like all the 
rest, of epithelial origin, according to Hatschek. A special 
diverticulum of the myocoelomic pouch pushes its way, at an 
early stage of development, between the muscle and the noto- 
chord, and also descends between the epidermis and the lateral 
plate (see PI. XXXVI ^4, figs. 6, 7). This outgrowth is called 
by Hatschek the sklerotome. 
It is indicated in the adult by a layer of connective-tissue 
cells of epithelial character, which surround the notochord, and 
a second layer, which rests on the surface of the muscular 
mass facing the notochord. Between the two was originally 
a space continuous with the myocoelomic pouch. This space 
is obliterated in part, but in part persists as the intra- 
skeletal or myoskeletal lymph-spaces of the myotomes. The 
disposition of these layers of cells will be best understood 
by a comparison of Hatscbek’s figures and tbe drawing of a 
well-stained section of an adult Ampbioxus (PI. XXXVI A , 
fig. 1). 
The sheath of the notochord deposited between the epithelial 
cells and the proper notochordal tissue is similar to the cutis in 
structure. Next to the notochordal tissue forming the inner- 
most layer of the sheath is a dense, highly-refringent substance, 
which gradually passes over into a more distinctly laminate 
layer (corresponding to the gelatinous layer of the cutis), and 
then follow the cells. In some preparations the staining of 
these two layers is very different ; in others they are not dis- 
tinguishable from one another. 
The dense innermost layer has been described by some 
observers as the cuticle of the notochord, just as the dense 
lamina below the epidermis is regarded as being formed by the 
epidermis cells. I am, on the contrary, inclined to reckon both 
to the connective tissue, and do not find in the adult Am- 
phioxus any recognisable and distinct notochordal cuticle, 
though such may exist in the embryo. 
The lamination of the connective tissue, both of cutis and 
notochord, will be best understood by the examination of 
figures 1 and 2 in PI. XXXVI A , as interpreted by the 
