806 MR EDWARD J. BLES ON THE 
may be seen faintly through the skin, and a swelling shows the position of the 
pronephros. 
All the preceding stages are still enclosed within the ege. We now pass on to. 
the larvee at the time of hatching. Fig. 16, Plate III, shows the larva at the normal 
stage of hatching with the vitellme membrane now enormously swollen out. The 
more or less thin layer of jelly which surrounds the membrane has not been drawn. 
Compared with the last stage illustrated (fig. 14), the muscular portion of the 
tail has grown, while the abdominal portion of it has become insignificant. The length 
of the tail (fig. 15a) is still only about half the length of head and trunk together ; 
the fin-fold has not yet become a powerful swimming organ. The head is now fora 
time divided from the trunk by a constriction, a neck, which is the more marked 
since the trunk is swollen just behind the constriction by the bulging of the skin 
over the pronephros (see fig. 16, Plate III). On the somewhat flattened anterior surface 
of the head the following can be made out (fig. 15, Plate III). On the ventral surface 
of the head is a conspicuous cement organ projecting downwards and forwards, 
exceedingly deeply pigmented at its base, so as to appear almost black. Running 
round the anterior edge of the protuberance is a clear-looking ridge with its outer 
end curved backwards; this is composed of the outer ends of the tall columnar 
cells of the cement organ filled with the cell-secretion. The oval patch behind the 
crescentic ridge is formed by the inner ends of the pigmented gland cells shining 
through the epidermis. The outline of the cement organ is thus crescentic and not 
circular, as Brpparp described it in his Xenopus tadpoles. Running up from the 
anterior border of the cement organ, and passing obliquely outwards, is the pair 
of bands of pigmented cells connecting the frontal gland with the cement organ. 
The cells of all three structures are found to be essentially similar when examined 
in sections, so that there is a continuous line of mucus-secreting cells enclosing an 
area shaped roughly like an inverted trefoil on the anterior surface of the head. 
The base of the trefoil above contains the paired rudiments of the nasal pits, and 
the apex contains the stomodceeum. The lateral bands of mucus cells are narrow 
and meet the ends of the broad transverse band which forms the frontal gland just 
internal to the level of the outer edge of the nasal pits, so that the nasal pits are 
bordered dorsally by the frontal gland. By comparing fig. 15 with fig. 10a 
(Plate I), it will be seen that the frontal gland is dorsal to the neuropore, and 
that the neuropore, if it persisted or if traces of it remained until this stage, 
would lie between the centres of the nasal pits. Another point worth notice is 
brought out by a comparison of the frontal view of these two stages, and that 
is the very close proximity of the neuropore to the small area from which the 
stomodceeum will be formed later in development. Taking into account the 
thickness of the ventral wall of the fore-brain, it will be seen how little space is 
available between the cement organ and the brain for the potential mouth at the 
earlier stage (fig. 10a). 
