hig 4 BYRNES. [VoL. XIV. 
are still in a very rudimentary condition. In the immediate 
region of the posterior limbs the myotome-processes are repre- 
sented only by afew embryonic cells at the ventral outer corner 
of the myotome (Pl. X, Fig. 13). — 
Fig. 15 represents a section through the posterior part of 
the body of a young Triton larva, some distance in front of the 
posterior limb. The myotome-process is represented by only 
a few cells at the ventral outer edge of the myotome. These 
cells are the forerunners of the primary abdominal muscle, with 
which they are connected in a more anterior section. One of 
the cells is shown in the act of dividing. Such cases of division 
are of frequent occurrence at the ventral edges of the myotomes 
in the posterior part of the body and are incidental to the 
growth of the abdominal muscle. 
Fig. 14 shows a section taken through the posterior limb- 
rudiment of a Triton embryo. The conditions shown at the 
ventral edge of the myotome in front of the limb (Fig. 15) 
differ in no way from those in the limb-region itself, except 
that in front of the limb the myotome-processes have begun to 
grow ventrally. On account of the close proximity of the pos- 
terior limb to the ventral edge of the myotomes, there is some- 
times an apparent connection between the two structures. 
Nevertheless, I believe this is only a coincidence, for, after 
having examined a large number of sections through the pos- 
terior part of the body, including the limb-region, I have been 
unable to find any special localized proliferation of cells from 
the myotomes to the limbs. Moreover, the number of dividing 
cells at the ventral edge of the myotomes in the limb-region is 
relatively very small. I cannot believe that in Amblystoma 
there is any ground for homologizing these single cells with 
muscle-buds when typical muscle-buds are absent. 
Among the higher groups of vertebrates, where muscle-buds, 
such as are found in the fishes, have not been shown to exist, 
the cells that are proliferated from the ventral edges of the 
myotomes have been very generally homologized with true 
muscle-buds. But the evidence given in these cases is not 
wholly convincing that the cells proliferated from the myotomes 
are really homologous to muscle-buds, or even that they give 
