372 
E. RAY LANKESTER. 
have not thought it desirable toreproduce that figure in the present 
memoir nor to produce one like it, but the reader is referred 
to the French naturalist’s drawing as one giving valuable data. 
An extremely important fact with regard to the fin-rays of 
the dorsal series is that they are between four and five times 
as numerous as the myotomes, and the question arises whether 
they have any definite numerical relation to the myotomes. 
I have counted from 250 to 260 fin-rays in an adult 
Amphioxus lanceolatus with sixty-one myotomes, no 
rays being developed over the last six. Supposing we exclude 
the imperfectly developed anterior and posterior regions, we find 
that there are very nearly 220 fin-rays for forty-five myotomes, 
approximately a relation of five to one. But I am unable to 
accept the view that there is any real relation between the 
metamerism of the fin-rays and the metamerism of the myo- 
tomes. The fact that anteriorly there are less than five fin- 
rays to a myotome, viz. four, and posteriorly more than five, is 
opposed to such a relationship, whilst further, the numerical 
features of the paired ventral fin-rays are entirely destructive 
of any theory of the kind, for we find in the ventral series (on 
an average) thirty-four pairs of fin-rays to twelve myotomes. 
The paired fin-rays of the ventral post-atrioporal mid-line are, 
like those of the dorsal series, contained in a series of compart- 
ments, which are divisions of a lymph-space. The space is 
not divided into a right and left half, but is simple. This 
lymph-space is continued as a contracted canal with 
coagulable contents along the mid-line posterior 
to the anus for the space of several myotomes. I am not 
able to say precisely where it terminates. A reinvestigation 
of the tail by transverse sections would at once settle this point. 1 
The number of the paired fin-rays varies a little. There are 
1 Anteriorly the dorsal fin-ray lymph-space ends with the notochord as a 
very contracted canal overlying it. It is of some importance to note that in 
this extreme anterior region there is a ventral lymph-space below the noto- 
chord of the same nature as that above it, but devoid of fin-rays, though 
divided into compartments, six in number. (See PI. XXXYI/f, fig. 3, and de 
Quatrefages.) 
