NOTE ON THE DEVELOPMENT OF AMPHIBIANS. 317 
crescent-shaped process immediately above the articulation 
with the Meckelian cartilage. This process extends to the 
base of the balancer separating the two blood-vessels which 
pass to and from the balancer. This process appears crescent- 
shaped only in vertical longitudinal section,, and the posterior 
blood-vessel lies partly enclosed in the crescent. The process 
is, shown at p. in the horizontal section, fig. 30h. Here also 
may be seen a bundle of muscle-cells extending from the 
pterygoid muscle (m.) into the base of the balancer ( bl .). 
Another band of apparently undifferentiated muscular elements 
passes from the end of the above-mentioned process down into 
the balancer. Section 30h is cut through the base of the 
balancer, the free end of which extends below the plane of the 
section. 
The balancers of Triton are of the same character as those 
of Amblystoma, but in Triton they appear to be not quite so 
highly developed. 
Clarke observed the use of the balancers in the living 
embryos, and came to the conclusion that the chief function 
of the organs was as a means of support for the embryos to 
prevent them from sinking into the slime on the bottom of the 
pools in which they live. My own observations on the living 
embryos have led me to the same conclusion. It seems there- 
fore that we have in this case not only the peculiarity of a 
homologue of the external gills arising from the mandibular 
arch, but also a homologue of the external gills becoming 
metamorphosed into an organ for the support of the body. It 
is also noteworthy that the balancers drop off after the limbs 
have appeared. 
If we seek among the Anura for organs homologous with 
these balancers of the Urodela, the only organs which we can 
fix upon with any degree of probability are the suckers of the 
tadpole. Balfour has stated that these suckers arise on the 
hyoid arch, but in the embryos of Anura which I have examined 
they appear immediately posterior to the mouth-fusion (fig. 20) 
long before any trace of a division into visceral arches has 
appeared. I think for this reason that the suckers cannot 
