756 MR FRANK J. COLE 
cannot be separated into units, and hence the intercellular substance here corresponds 
with the cement of the hard cartilage, so that we have at once a sharp morphological 
distinction between the hard and soft cartilages. This distinction, however, only partly 
applies to Myxine, for in places we find in the soft cartilage a deposit of secondary 
ground substance, and generally cell capsules are differentiated. The soft cartilage of 
Myaine, therefore, represents a stage further than that of the lamprey. There seems 
to be no question that the hard cartilage of cyclostomes, both as regards its minute 
structure and micro-chemical reactions, may be directly compared with the hyaline 
eartilage of other animals. 
In addition to ScHAFFER’s memoir, the cartilage of cyclostomes has also been 
investigated by Srupnicka.* This author finds the cartilage of the tail fin to represent 
an intermediate type, which I can confirm ; but there must be added thereto the cartilage 
of the branchial skeleton. There is thus no break between the two kinds of cartilage, 
and this discontinuity is more in evidence in Myaine than in the lamprey. Stupnicka 
doubts the presence (normally) of the cell capsule of Scoarrer in Myaine; and whilst 
it is indeed true that there is a conversion of the capsule into ground substance in some 
cases, as in higher animals, my fig. 3, which was drawn before I had seen the papers 
of either author, amply confirms ScHAFFER in this respect. STUDNICKA was the first 
to examine what I have described below as the pseudo-cartilage of Myxine, which he 
terms ‘“‘vorknorpel,’ and of which he correctly asserts, on account both of its mor-. 
phology and micro-chemical reactions, that it cannot be regarded as true cartilage, but 
is a transition tissue. SCHAFFER, in his later paper, compares it with the tissue of 
the sesamoid nodule in the Tendo Achillis of the frog, and states that, whilst he does 
not regard it as true cartilage, it nevertheless exhibits considerable resemblances to the 
simplest form of true cartilage. He considers the posterior segment of the basal plate 
as a true sesamoid formation in the tendon of the M. retractor linguze,t and its cells 
as peculiarly modified tendon cells. This has been independently stated by Ayzrs 
and Jackson, evidently without knowledge of ScuarrrR’s work, and is clearly the 
correct view. In this connection [ may mention that, in the cells of the frog's 
sesamoid above, Mrves was able to establish the presence of centrosomes, and this 
induced ScHarFeR to look for them in the similar tissue of Myaine. He succeeded in 
his quest,{ and found that the cells of the posterior segment of the basal plate contained 
one or two centrosomes, each surrounded by a clear area. I can confirm this discovery, 
and am able to extend it to the cells of the hard cartilage, as shown in fig. 3. 
Paraffin sections of the skeletal tissues of Myxine are invariably distorted and 
unreliable, and hence the histology of the skeleton is best studied by means of free- 
hand sections stained preferably with Mawnwn’s methyl-blue-eosin. Provided care is 
taken to avoid being misled by certain deceptive appearances incidental to thick hand 
* A. fm, A., 48, 1896, p. 606. Also 51, 1898, p. 452. 
+ This is surely a slip of the pen. The muscle should be the M. copulo-copularis, P. FURBRINGER (M. constrictor 
musculi mandibuli, Ayers and Jackson). 
t Siz, K. Akad. Wren, Abt. iii., 105, 1896, p. 21. 
ie 
