508 
that, owing to the early wandering of cells from the walls of the 
mesodermic somites and the close approximation of these cells to the 
ectoderm, the important part played by the ectoderm in the proli- 
feration of mesoderm for the formation of cartilage cannot there be 
traced as easily as in Necturus. Nevertheless, KASTSCHENKO !) has 
observed the contribution of ectoderm to mesenchym in Elasmobranchs, 
and GORONOWITSCH ?) notices a similar proliferation of ectoderm in 
the bird in tho region of the nose, mouth, and branchial clefts. 
In this connection I would call attention to a proliferation of 
ectoderm cells into the mesoderm noticed by OrperL?) in Anguis 
fragilis, and by my self‘) in Batrachus, and confirmed by the 
observations of H. B. PoLLArn on many forms of Teleosts at the 
Naples station. The proliferation to which I refer is immediately back 
of the eye. It was interpreted by me (loc. cit.) as indicative of a 
lost gill-cleft, which may still be true, though the proliferation doubt- 
less has reference to the dense mass of cells which be immediately 
below it, and which constitute what Stönr>) calls “den Boden, in 
welchem sich der Processus pterygopalatinus entwickelt”. 
I would add that (as has been observed in several other Verte- 
brates) a large part of the sheet of neuralcells which lies above and 
at the side of the first and second primary cerebral vesicles, and 
which in part forms the Anlage of the Trigeminus group, breaks up 
in Necturus into stellate mesoderm. What role these cells play in 
the formation of later tissues I do not know, nor do I know what 
becomes of the “lost” portions of the neural crest which lie between 
the spinal ganglia, but it has become evident that the whole question 
of the nature of “mesoderm” in Vertebrates needs revision founded 
on fact rather than theory, and I doubt our right to coordinate 
1) N. Kasrscuenxo, Zur Entwickelung des Selachierembryos. Ana- 
tomischer Anzeiger, Bd. III. 
2) N. GoronowıtscH, Die axiale und die laterale Kopfmetamerie der 
Vogelembryonen. — Die Rolle der sog. “Ganglienleisten” im Aufbau der 
Nervenstimme, Anatomischer Anzeiger, Bd. VII. 
3) A. OrreL, Ueber Vorderkopfsomiten und die Kopfhöhle von 
Anguis fragilis. Archiv f. mikrosk. Anatomie, Bd. XXXVI. 
4) Jura B. Pıart, Further Contribution to the Morphology of the 
Vertebrate Head. Anatomischer Anzeiger, Bd. VI. 
The double nature of the mouth involution mentioned in this paper 
was independently observed by me. Priority in observation, however, 
belongs to Miss CorneLıa M, CLapr. 
5) P. Ströme, Zur Entwickelungsgeschichte des Kopfskeletes der 
Teleostier, Leipzig 1882. 
Be, = ere 
