124 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
during ontogeny, and that those of the Marsipobranchii 
are replaced in horny successors, 1t is imperative to 
enquire whether the vanishing teeth are in the two types 
homologous. 
The calcified teeth discovered by Beard in the Marsi- 
pobranchii lie, in all cases, beneath the familiar horny ones. 
Behrend has supplemented Beard’s account of these 
structures in some details, and has recorded* his inability 
to discover that ‘“‘enamel cap’’ described by him; and I 
personally doubt the very densely calcified nature of the 
teeth, upon which Beard lays stress. That which is most 
conspicuous however about these structures is their re- 
moteness from both the jaw apparatus and all parts such 
as could conceivably represent that; wherefore it 1s highly 
improbable that they answer to the actual maxillo-mandi- 
bular teeth of the higher gnathostomata. 
That the calcified teeth of the vertebrata are but in- 
turned (mouth) scutes is certain ; and in many Selachians 
(ex. Cestracion, Carcharias) nearly the whole of that part 
of the stomodw#al membrane which does not invest the 
jaws is besett (Pl. X, fig. 7) by a series of smaller scutes. 
These are for the most part unrepresented in the higher 
vertebrata; but the presence of a uniformly diffused series 
of minute denticles over the inner faces of certain bones 
bounding the mouths of some of the higher fishes (ex. the 
palatines,. pterygoids, and splenials of Amza),{ in the 
light of Hertwig’s observations$ concerning the origin of 
the vomer, palatine and operculare (splenial) of the 
* Zoolog. Anzeiger, 1891, p. 86. 
+Conjointly with more or less of the pharyngeal (gill bearing) region. The 
presence of calcified denticles in the latter area is strongly suggestive of an 
inward proliferation of the epiblast, such as Beard has invoked in seeking to 
explain (Spengel’s Zoolog. Jahrb, Bd. cit., p. 764) the origin of the taste buds. 
tef. also Giinther ‘‘ Study of Fishes,” p. 124. 
gArchv. f. Mikr, Anat, Bd. XI, p. 108 (supplem.). 
