AMPHIOXUS LANOEOLATUS. 
379 
alimentary tract to which the body wall so closely moulds 
itself. The relation of these parts is shown in PI. XXXIV, 
fig. 1, and it is clear enough that we cannot in the prse-atrio- 
poral region separate the various parts of the enteric canal 
from the closely adherent body wall. The csecum appears not 
to be enclosed in a portion of body wall common to it and the 
pharynx ; but there is actually a complete diverticulum of the 
body wall covering, and fitted to, the csecum, leaving a small 
coelomic space between the somatic and splanchnic elements, 
as shown in PI. XXXVI. 
I do not propose to enter on the present occasion into detail 
with regard to the structure of the successive regions of the 
pharynx, but I may point out that whilst in the anterior region 
it is broad and heart shaped, in section it becomes posteriorly 
greatly compressed, as shown in PI. XXXVI. This shape 
appears to me to be the natural shape during life; when the 
gouads are enlarged the pharynx is necessarily compressed 
throughout that region where it is accompanied by the 
caecum. 
The numerical relation of the caecum appears to be as 
follows : — It is given off as a diverticulum on the right side of 
the body about the 28th or 29th myotome, and reaches as far 
forward as the 15th or 14th myotome. These figures apply to 
adult specimens. 
The vascular system of Amphioxus appears to be in a con- 
dition of degeneration, since it presents a certain limited 
development of vascular trunks, which do not appear to have 
a physiological significance in their present relations. 
I am not in a position to give a critical account of 
the vascular system, but it is necessary to draw attention 
very emphatically to the continuity of the vascular trunks 
and lymphatic spaces of Amphioxus and their contents, 
which make it impossible to decide with certainty in all cases 
whether a given space with coagulable liquid contents is to be 
considered as blood-vessel or lymph-vessel. Such a communi- 
cation is described by Schneider and figured by him, showing 
the free connection of the veins of the csecum with the dorso- 
