366 
E. RAY LANKESTER. 
definitely exhibiting the position and form of the brown funnels, 
is (1) to furnish a few numerical data of importance for the 
anatomical discussion of Amphioxus ; (2) to correct some 
errors which appear to be current as to the existence or non- 
existence of spaces of one kind and another in the body and 
gill-bars of Amphioxus; and (3) to submit some drawings 
which represent, in a semi-diagrammatic form, the structure 
of Amphioxus, not merely as seen in sections or dissections, 
with all the imperfections necessarily arising from the action 
of preservative media, but as reconstructed and corrected from 
numerous specimens, so as to give as nearly as may be a true 
conception of the undistorted organism. 
External Marks and Numerical Characteristics. 
The general outline and form of a living specimen of 
Amphioxus lanceolatus is given in PI. XXXIV, fig. 4. 
The drawing is constructed from sketches made by me at 
Naples from the living animal, and has been corrected by sub- 
sequent study of preserved material. When Amphioxus is alive 
and at rest the atrial chamber is dilated in such a way that its 
median ventral surface projects below the two lateral ridges, 
for which I have proposed the name “ metapleura. ” I doubt 
whether in life this surface is ever contracted to the extent 
which it is in even the most carefully preserved specimens, 
such, for instance, as that shown in PI. XXXV, fig. 3. That 
specimen was treated with Kleinenberg's picro-sulphuric solu- 
tion, followed by increasing strengths of alcohol ; and I have 
not yet found any treatment which gives a less general distor- 
tion of the body than this. Specimens placed when living into 
alcohol assume the most extreme distortion, owing to the vio- 
lent contraction of the transverse ventral muscle of the atrial 
wall, and the shrinking of tissues and spaces. Such an extreme 
contraction is exhibited in the figures of Rolph’s important 
treatise on Amphioxus (3), and to a less extent in figs. 2 and 3 
of PI. XXXIV accompanying this memoir. In PI. XXXVI 
I have given a diagram of a transverse section with such form 
and proportion of all regions and spaces as I have been led to 
