542 FRANOIS VILLY. 
surface, maintaining relations with the future annular 
cartilage. 
The peculiar development of this organ in the lowest forms 
with such a structure raises a question: Are the hyomandi- 
bular cleft and Eustachian tube homologous? If I am correct 
in stating that there is no connection between the two organs 
at any period in the frog’s history, there is obviously strong 
reason for doubting the generally accepted doctrine of their 
homology. But it may be said that the frog’s development is 
modified in this particular point, and that as the two first 
visceral arches have a peculiar history in which they probably 
undergo great larval modification, so they have modified the struc- 
ture placed between them, i.e. the hyomandibular cleft. The 
mandibular arch in its early movement, and the hyoid arch by 
its articulation with the mandibular arch, might cause the 
hyomandibular cleft to develop in a peculiar way, so that it 
disappears at one time and again reappears. This is not 
impossible, for in the second stage described the Eustachian 
tube occupies a position between the mandibular and hyoid 
bars at their point of articulation, and thence its runs forwards. 
Such a course would be peculiar for the hyomandibular cleft, 
but when the relations of the arches concerned are considered, 
it will be seen that the early position of the Eustachian tube is 
not irreconcilable with the view that it is morphologically the 
hyomandibular cleft. The second point in the development of 
the tube, that is its breaking up into pieces during the 
metamorphosis, may possibly be explained as being due to 
mechanical causes originated by the movement of the hyoid and 
mandibular arches at the time. As far as the considerations 
advanced go, it is justifiable to hold that the frog’s development 
does not absolutely disprove that the Eustachian tube and hyo- 
mandibular cleft are homologous, although they are probably not 
connected in development. This view would be in accordance 
with the doctrine generally held, although a not unimportant 
section of investigators have considered that actual embryology 
does not bear out the doctrine usually taught. At the same time 
it should be remembered that the evidence offered by the frog— 
