750 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
maxillee and maxillee develop in advanced embryos as paired translucent rods (PI. XI. 
fig. 20), which gracefully curve, like bars of chitin, below the eyes forward to the 
ethmoidal region, and form the sole lateral supports of the oral roof (Pl. X. fig. 1; 
Pl. XIII. fig. 7). They are essentially superficial, and lie in a thin stratum of membrane 
which stains deeply, called by Poucuer “ tissue générateur,” and occupying the situation 
of Parker’s “ subocular bands,” though he regards them as the rudiments of the pterygo- 
palatine arch (No. 117, p. 113). The homology of these dermal maxillary rods, with the 
labial cartilages of more primitive forms, as suggested by Dr GUnrueEr (No. 61, p. 90), 
is of much interest. A pair of curved bars, probably palatine elements, are also developed 
in the roof of the oral chamber at a late embryonic stage. They are irregular in thick- 
ness, slightly curved, and attenuated at the extremities (PI. XI. fig. 18). 
When first distinguishable, the pharyngeal bars consist simply of solid mesoblastic 
thickenings passing along the lateral and ventral walls of the mouth, and more or less 
oblique in direction ; moreover, in cross-section, these thickenings are found to be paired, 
and united in the middle line, forming a roof over the pericardial chamber (PI. XI. 
figs. 1-3, 6-8). The cells assume a columnar arrangement, and constitute lamine, 
which appear as parallel superposed strata, when the bar is cut longitudinally (Pl. XI. 
fig. 9), but in a cross-section of a bar these strata are observed to be somewhat concentric 
and laminated (Pl. XI. figs. 6-8). Each rudiment of a branchial arch (fg, Pl. XI. 
figs. 6-8), when fairly defined, consists of a cylindrical mass of cells, concentrically 
arranged round the central point of the bar, and limited above by the epithelial hypoblast 
of the pharynx, and below by the pericardial hypoblast. They increase in length, and 
change from the transverse to the antero-posterior oblique position (PL VIII. fig. 9), the. 
inner extremity of each pair of arches apparently shifting forward, so that they point 
anteriorly (Pl. X. figs. 2, 3, 5); while their upper and posterior parts, which extend 
up the lateral walls of the pharynx, have moved very slightly from their primary position. 
Neither the mandibular nor the hyoidean arches are so markedly transverse in situation as 
the branchial bars proper, and they alter very little in position as development proceeds. 
In the gurnard, three days old, at the anterior end of the hyoid arches, 7.e., where the 
copula is formed, a large boss occurs, formed chiefly by a free development of the lining 
membrane of the oral floor, This membranous expansion (really a lingual rudiment) pro- 
jects as a large irregular elevation on the floor of the mouth, and is lifted up by the 
erratic movements of the hyoid arch, as though the operation of deglutition were being 
performed (Pl. XIV. fig. 2). Gradually the arches lose their dense indifferent appear- 
ance, and become converted into cartilage, the small primary cells being broken down, so 
that each bar consists of larger flattened elements placed transversely, and giving the 
arches a transversely striated appearance (PI. IX. fig. 5). The flattened cells become 
hyaline, and each arch shows a single column of hyaline discs contained in a thin peri- 
chondrial membrane. The first two arches wholly assume this character, and are seen to 
be composed of these discs or chondroplasts placed one above the other along the 
whole length of each bar (see the figure just referred to); but in the four arches which 
