ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 755 
is arranged in concentric layers round each cell cavity. Here and there two such 
cavities are surrounded by the same concentric layers. This concentric structure seems 
to me to be due to the nature of Rerzrus’ sections ; but whatever its explanation may 
be, no subsequent observer has confirmed Rerzius’ description. 
W. K. Parxer describes four varieties of skeletal tissue in myxinoids, which 
correspond to my hard and soft cartilage and pseudo-cartilage below, as far as I 
understand his description. The hard cartilage, he says, has a “ greenish” colour. 
Ayers and Jackson state that the whole of the cartilage (preserved in formol) assumes 
a “pink or reddish tinge,” and this, together with their somewhat remarkable neglect 
of the literature of the subject, accounts for the failure of these authors to detect 
one of the most obvious and striking characteristics of the myxinoid skeleton. Howes 
regards the distinction between the two kinds of cartilage as a “subtle” one; but the 
difference, as we shall see, is very real. PotLarp* describes the hard cartilage of Myaine 
as consisting of ‘only a hard yellow spongework of the intercellular matrix,” the 
) 
nuclei and protoplasm of the “ procartilage” cells having disappeared. I have, 
fortunately, had an opportunity of examining the sections on which this statement 
was based, and find that as the material was stained in bulk with picro-carmine, the 
stain has reached the cartilage cells in the soft or more penetrable cartilage ; but that 
the cells of the hard or denser cartilage are not stained, whilst the intercellular substance 
is coloured yellow. With the low power, therefore, PoLtLarn’s description appears 
correct ; but examination only with a Zeiss D at once reveals the cells in the hard 
cartilage, as shown in fig. 3, so that PoLLarn’s description is inaccurate. 
The most reliable description of the cyclostome skeleton we owe to ScHAFFER,t 
most of whose points I had made out quite independently before I had an opportunity 
of consulting his work. The following abstracts, therefore, may be taken as including 
my own results also. All the fresh cartilage is white and uncoloured, but the hard 
cartilage is. more opaque. ‘The red colour assumed by the latter arises gradually in 
alcohol first on the surface and then penetrates inwards. I have, however, so far not 
found the red colour supervene on formol preserved material. The hard cartilage may 
be said to consist of a number of units each composed typically of one cartilage cell 
(ct. c.), a cell capsule (c. ct. c.), and a ring of secondary ground substance (s. g. s.), 
these units being held together by a cement substance (c. sb.), from which, however, 
they may be macerated out. I find that the independence of these units is more marked 
in some places than in others; for instance, in the palatine bar there is a complete ring 
of cement round each unit, as described by Scuarrer, whilst in parts of the middle 
segment of the basal plate these rings are by no means complete, as shown in fig. 3. 
Hence maceration here has not been successful. In the lamprey, according to SCHAFFER, 
the intercellular substance { of the soft cartilage forms a continuous network which 
* 1894, p. 349 ; and 1895, p. 415. 
+ Z. f. w. Z, 61, 1896, p. 606. A. f m. A., 50, 1897, p. 170. 
t ScHarrer’s term for the non-protoplasmic portion of the cartilage. 
