406 
E. RAY LANKESTER. 
Fig. 2. — Portion of a transverse section of Amphioxus, to show the 
metapleur and the region of the supposed “ ventral canals ” (non-existent). 
The various structures shown are named on the drawing. A small artifact 
space is seen between the transverse muscle and the thick gelatinous layer of 
the cutis, which is similar in position and origin to larger rents which have 
led to the erroneous inference of the existence of “ ventral canals.” The 
nuclei of the transverse muscle and the vertically fibrillated non-nucleated 
structure of the gelatinous layer of the wall of the metapleur are noteworthy. 
The same fibrillated structure is seen in the gelatinous layer of the cutis in 
other sections through other parts of the body wall, especially where the 
transverse intermuscular septa join the sub-epidermic cutis. 
Pigs. 3, 4, 5. — Three vertical sections through the anterior extremity of 
Amphioxus, the first in front of the termination of the nerve-cord, the 
second through the olfactory pit, and the third through the eye-spot. The 
drawings were made by Mr. Herbert Thompson, M.A., in the zoological 
laboratory of University College. 
a. Pin-ray lymph-space. b. Cavity of the neural sheath or skeletal tube 
in front of the termination of the nerve-cord, occupied by a clot. c. Anterior 
nerves in transverse section, d. Notochord, e. Sub-notochordal lymph- 
space, probably similar in nature to the dorsal fin-ray lymph-space, f. Irre- 
gular lymph-spaces lined with connective-tissue epithelium, excavated in the 
gelatinous tissue of the dorsal and ventral fin-plates, g. The ventral prae- 
oral fin-plate, becoming here the right half of the prseoral hood. h. The 
unequally developed left-side outgrowth, which becomes the left half of the 
praeoral hood. i. The ciliated olfactory pit, an inversion of the epidermis of 
the left side, connected with a short olfactory bulb or nerve given off from 
the left side of the nerve-cord. k. The wall of the nerve-cord enclosing the 
enlarged neur-axial canal. /. The eye-spot, consisting of distinct spherical 
granules of brown-black pigment, m. The unobliterated myoccelomic pouch 
of the first myotome, identical with the cavity marked m. in Pig. 7- n. The 
muscular epithelial cells of the mediad wall of the pouch, o. The myoccelomic 
pouch of the second myotome. 
Pig. C. — Diagram of a transverse section through an early larval condition 
of Amphioxus, showing the division of the primitive coelomic pouches into a 
dorsal myoccel and a ventral splanchnoccel. The origin of the cutis 
from the peripheral and of the muscular tissue from the mediad wall of the 
myoccel is indicated. Prom Hatschek. 
Pig. 7. — Diagram of a transverse section through a later larval condition 
of Amphioxus, showing the origin of the skeletal tissue from a secondary 
pouch, “ the sklerotome,” which grows out from the myoccel and pushes its 
way between the notochord and mediad muscular wall of the primitive myoccel, 
and downwards between the wall of the splanchnoccel and the epidermis. 
Prom Hatschek. 
