Charles R. Stockard 493 
again the mandibular cleft turns ventro-laterally; and, as before, the 
entire tissue below the cavity of the throat is the dental-plate anlage 
corresponding in position and extent to the lower jaw tissues of all 
vertebrate embryos. From these figures one might suggest that the 
median body may still represent a tongue, but it will at once be seen 
that the sections pass through the region of the hypophysis and are thus 
anterior ones. They are obviously too far in front of the hyoid cleft 
to represent the tongue anlage. I have looked with the greatest interest 
hoping to find some indication of a tongue in these embryos, as | would 
then be assured that the other apparatus was certainly not such an 
organ. My failure to find it, however, is not surprising in view of the 
fact that the tongue is inconspicuous in most fishes, and may even be 
entirely wanting in some. It may not be out of place to recall here 
that the fish’s tongue is essentially a projection of the forward part of 
the hyobranchial apparatus with the mucus membrane of the mouth 
covering the thickened submucosa. Its development is, therefore, inti- 
mately connected with that of the skeleton. 
Fig. 9 shows the condition of the dental-plate as illustrated by a 
section passing through the anterior part of the organ. In this embryo 
the gills are completely drawn into their position on the sides of the neck, 
i. e., not spread out laterally as in the previous stages. They have 
shifted a considerable distance back of their original position, so that 
a long interval now exists between the hyomandibular cleft and the first 
branchial gill. In none of the embryos mentioned above had any shift- 
ing of the gills taken place. The gill pouches it may here be noted 
are just beginning to be formed, a process which will be described further 
on. This embryo is also interesting as being the youngest one in which 
the anlage of the thyroid gland makes its appearance, Stockard, 06. 
The anterior ends of the fore-gut and of the nasal canal are directed 
ventrally and they are now more caudad in position than when fully 
developed. 
The two lateral prongs of the dental-plate anlage have grown further 
forward than the median copular portion and are seen to have become 
thicker dorso-ventrally, as has, also, the entire head of the embryo. For 
this reason the mandibular cleft has now a strong curve. but still comes 
in intimate contact with the ventral body wall, being prevented from 
opening to the outside only by the secondiire Rachenhaut of Kupffer. 
Two median tentacles are seen below in cross section showing their 
cores of mesoderm stippled. As we pass caudally in this same embryo 
to a place shortly anterior of where the Nasenrachengang, Hp, opens 
into the throat we find such a section as is seen in Fig. 10. This shows 
