RELATIONSHIP OF AMMOCG:TES TO OSTRACODERMS 333 
In Fig. 132, B, I give a specimen of this tissue stained by osmic 
acid; in Fig. 132, A, I give a drawing of ordinary muco-cartilage 
taken from the plate of the lower lip; and in Fig. 133, A, a modifi- 
cation of the muco-cartilage taken from the velum, which shows the 
formation of a tissue in- 
termediate between ordi- 
nary muco-cartilage and 
this branchial fat-tissue. 
Further, in fully-grown 
specimens of Ammoccetes, 
in the region of undoubted 
muco-cartilage, a fatty de- 
generation of the cells 
frequently appears, to- 
gether with an increase 
in the blood spaces,—the 
precursor, in fact, of the 
great change which over- 
takes this tissue soon 
afterwards, at the time of 
transformation, when it is 
invaded by blood, and 
swept away, except in 
those places where new 
cartilage is formed. I 
conclude, then, that the 
tissue of this vascular 
space was originally muco- 
cartilage, which has de- 
generated during the life 
of the Ammoccetes. The 
fact that in most. cases 
undoubted muco-cartilage 
Fig. 182.—A, Muco-cartinace of Lowsrr Lip 
(Mc.); m.ph., muscle of lower lip; m.sm., 
somatic muscle; Cor., laminated layer of skin. 
B, DEGENERATED Mvco-CARTILAGE OF Bran: 
cH1at Recion. F., fat layer; P., pigment; 
Bil., blood-space; N., somatic nerve; m.br., 
branchial muscle; m.sm., somatic muscle. 
is to be found here and there in this space, is strong confirmation of 
the truth of this conclusion. 
If this conclusion is correct, we may expect that it would be 
confirmed by the embryological history of the tissue, and we ought 
to find that in much younger stages a homogeneous tissue of the 
same nature as muco-cartilage fills up the spaces in the branchial 
