MUSEUM OF COMPARATIVE ZOOLOGY, 125 
The myotomie projections here described are observed in the three 
anterior myotomes ; but in the posterior region of the pectoral plate, 
i.e. the region of the fourth myotome, no such distinct cell-mass is 
produced prior to the connection of myotome and pectoral plate. The 
process in this region seems to consist from the first in the passing 
over of individual cells into the pectoral plate (prf. my’tm., Figs. 48, 
49, and 50). 
It is highly probable that the projection of the ventral portion of 
the myotome is due in part to the tendency of the myotomes at this 
stage to fold upon themselves. This tendency can be readily seen in 
sections back of the pectoral region (Fig. 44), and is the result of the 
relatively large amount of yolk in the Teleostean ovum, causing not 
only the lateral layers, but also the lower portion of the myotomes, 
to present the appearance of being pressed upward and outward. 
While it is true that myotomes back of the pectoral region, as well 
as those adjacent to the pectoral plate, show this tendency of their 
ventral portions to project outward, two points of difference must be 
noted. (1) In the pectoral region the myotome extends outward 
relatively much farther than in the post-pectoral region (compare 
Figs. 44 and 47) ; and (2) the peripheral layer of this projecting por- 
tion of the myotomes in the post-pectoral region consists of a layer only 
one cell in thickness, similar to that of the upper and outer boundary 
of the myotome, whereas the laterally projecting portion of the myotome 
in the pectoral region, prior to its connection with the pectoral plate, 
consists of a mass of indifferent cells, equivalent to a layer three or four 
cells in thickness (compare Figs. 44 and 47). This condition of the 
myotome and the accumulation of this mass of indifferent cells cannot, 
therefore, be regarded as insignificant, or common to all regions of the 
trunk, but must be looked upon as a growth leading to the contribu- 
tion of elements to the pectoral plate. I am at present undecided 
whether any distinction should be made between the earlier contri- 
bution of elements, which is in the form of a mass of cells, and the 
later, which consists of single cells. It seems to me, however, to be 
beyond doubt that in both cases the source of the elements is the pe- 
ripheral layer of the myotome, the cutis-plate, and I am inclined to 
believe, both from this and from the fact that in the posterior pectoral 
region the contribution seems to be from the beginning by single cells 
only, that the latter form may be regarded as a modification of the ear- 
lier and more conspicuous method. 
In addition to this contribution from the muscle plates, it is highly 
