440 



Mr. W. K. Parker. 



[Jan. 11, 



the Myxinoids and related types have been absolutely necessary to me. 

 T shall be proud if this and the next paper are thought worthy of being 

 considered an appendix to his incomparable works on these types. 



But as regards the Marsipobranchs generally, especially the 

 Lamprey, I am deeply indebted to Professor Huxley's writings and 

 to discussions with him upon these fishes ; and in the same way to 

 the late Professor F. M. Balfour, F.H.S. ; and I am indebted further 

 to my young friend Mr. W. B. Scott, of Princeston, U.S., who, 

 after Calberla, has worked largely on the early development of the 

 Lamprey. 



What I have been able to make out with regard to the skeletal 

 parts of the Lamprey will be offered to the Royal Society very soon, 

 and then the structure of the adult Myxinoids and of the various 

 stages of the Petromyzoids can be compared together. 



But the various kinds of the " Anurous Amphibia " — hundreds of 

 species — give us, in their larval state, a sort of temporary generalised 

 Marsipobranch fish ; it is not unknown that I have given several years 

 of labour to these types, and I feel now that I may, with caution, 

 attempt to explain the morphology of the skeleton in all these three 

 related groups — the Myxinoids, the Petromyzoids, and the Anura. 



However far apart, now, these three groups may be, they are 

 seen to be the nearest of kin to each other when we consider the 

 other " Ichthyopsida." Moreover, they form a curious scale, so to 

 speak, one rising above the other in a regular order ; for the Myxinoids 

 are a sort of arrested Ammocoete or larval Lamprey, and the Lamprey 

 in its adult state is quasi-larval if it be compared with the anurous 

 amphibian — Frog or Toad. 



The Myxinoids are very anomalous, and this is seen even in their 

 histology; in them, as in the Lamprey, there are two kinds of cartilage 

 — one very dense and almost as hard as bone, and the other soft, like 

 the cartilage of young embryos of higher types. 



But in the Myxinoids one very large bar, the great basi-branchial, 

 is formed of a light, elastic, vacuolar tissue, but little denser than 

 that of their great persistent non-segmented notochord, and, like it, 

 ensheathed in a very thick web of fibrous or tendinous tissue. 



I suspect that this fact will have a meaning for the student of the 

 lower non-craniate " Chordata " — Amphioxus, the Ascidians, &c. 



In the wide-mouthed, non-suctorial larva? of the Cape Toad (Daciyl- 

 ethra) — I found the whole chondro-skeleton composed of a peculiar 

 kind of cartilage intermediate between hyaline cartilage and this 

 vacuolar tissue of the Myxinoids ; it is more like the pith of a plant 

 than like ordinary cartilage. 



In their cranio-facial skeleton the Myxinoids are very remarkable ; 

 where segmentation is perfect in other piscine types they only 

 exhibit a lattice- work of continuous growth ; in the median region of 



