AMPHIOXUS LANCEOLATUS. 
393 
It is pointed out that the dorsal pouches enclosing each a 
“ myoccel 55 undergo the following modification : — The parietal 
Avail (subjacent to the epidermis) becomes cutis, and is called, 
therefore, the “ cutis-layer, 5 ’ whilst epithelial cells of the 
mediad wall (adjacent to the notochord) become individually 
elongated and converted into muscle-cells. The cavity of the 
myoccel remains for a time, and the muscular tissue is a truly 
epithelial tissue. 
Professor Hatschek does not deal with the adult animal. It 
may therefore be stated that the myoccel cavities totally dis- 
appear in the full-grown Amphioxus, excepting at the extremi- 
ties of the body. Some of the spaces, which are invariably to 
be found in transverse sections of Amphioxus between the 
connective tissue and the muscular masses of the myotoms, are 
artifact, and due to the contraction of the muscular fibre. 
These spaces can be distinguished from the natural intra- 
skeletal lymph-spaces of the myotomes (first described and 
figured by Schneider) by the fact that they are not limited by 
connective-tissue epithelium. 
Professor Hatschek states that after the myoccel is formed a 
secondary pouch forms by a folding inwards and upwards of 
the ventral wall of the myocoel, which, as development ad- 
vances, makes its way as a double fold between the notochord 
and the muscle-layer, Avhilst at the same time the pouch grows 
downwards between the lateral plate (the cavity of which is 
the splanchnocoel) and the epidermis. The cells of this offset 
of the myoccel pouch give rise to the skeletal tissue, Avhich 
invests the notochord and the nerve-cord, as well as the fin- 
rays, the cavities of which are part of the myocoel, whilst it 
also furnishes the fascia to the muscle-fibres. The arrange- 
ment is explained by the two diagrams in PI. XXXVI A, 
figs. 6 and 7, copied from Hatschek 5 s paper. In the adult 
Amphioxus the space between muscle fascia and notochord 
sheath persists as a series of large lymph-holding spaces in 
connection with the roots of the spinal nerves (see PI. XXXVI 
and PI. XXXVI A, fig. 1). The walls of the space become 
adherent in parts, but leave considerable regions as cavities 
