784 MR FRANK J. COLE 
material the fin rays and the pulsating caudal heart are plainly visible. In front of 
the cloaca there is an adipose median pre-anal fin, with no skeleton (‘‘ fin” 8). 
It is very surprising that although J. Mtuier dissected the tail of Bdellostoma, he 
should have failed to recognise its skeletal features. In a brief reference * he describes 
the median cartilages as fibrous vertical sheets—that is, merely local thickenings of the 
fibrous septum separating the two halves of the body musculature. ScHNEIDER, in 1879, 
for the first time briefly describes the caudal skeleton of Myxine and Bdellostoma ; and 
CLELAND,t unaware of SCHNEIDER'S work, subsequently published two descriptions of 
Myxine. These are, however, very inaccurate. The first detailed account of the tail of 
a myxinoid was published by G. Rerzius,t whose work I can confirm except in some 
minor points. 
Myxime possesses, as far as external features go, a diphycercal caudal fin. 
When, however, a dissection of the tail is made it is seen that the notochord (nt.) near 
its extremity takes a slight downward turn, and that its tip is buried in a median vertical 
sheet of cartilage (m. d. b., m. v. b.) which in front splits up dorso-ventrally so as to 
extend forwards under the notochord, over the neural tube, and also slightly between 
these two structures. This cartilage is unevenly distributed above and below the 
notochord, passing further forwards above and being deeper below. To it are fused, 
above and below, the posterior fin rays (f. r.), which are, of course, not comparable to the 
true fin rays of the higher fishes, the whole apparatus being characteristic of the 
myxinoids. J. MU Lier and Ayers and Jackson describe an imperfect segmentation of 
the fin rays of Bdellostoma as in the bony fishes, but I have seen no traces of this in 
Myzxine. Further, there is no indication of a segmental arrangement of the fin rays, 
except anteriorly. The cartilage partly encloses the bulbous extremity of the neural 
canal (containing the enlarged termination of the spinal cord), since the latter extends 
further backwards than the notochord. It may be conveniently divided into the 
following two portions :— 
Median Dorsal Bar (m. d. b.).—This is narrower than the median ventral bar, but 
extends further forwards. The posterior portion of it is attached in the middle line by 
an expanded base to the roof of the neural tube ; but the anterior half is lifted up above 
the neural tube, and is there merely a thin bridge of cartilage connecting up the bases 
of the fin rays. There were forty eight fin rays connected with this cartilage in the 
specimen figured. Rerzrus gives about thirty for Myaime, and Ayers and JACKSON 
twenty-five to forty for Bdellostoma. 
In front of the median dorsal bar there are about forty-five free fin rays not con- 
nected with any longitudinal cartilage, but inserted by their bases into the septum 
between the two halves of the body musculature and connected by fibrous tissue. In 
Bdellostoma, according to AyERS and Jackson, the anterior dorsal fin rays have such 
expanded bases as to almost complete the dorsal bar in front. There are apparently 
* Op. cit., p. 91. + Fourth Ann. Rep. Fish. Bd., Scotland, 1885. Also Rep. Brit. Assoc., 1885. 
t{ For the comple‘e paper, see Biol. Unters., vil., 1895, p. 26. 
