BY MOLECULAR COALESCENCE. 135 
can be seen with the larger ones, then the nature of the 
appearance becomes obvious. Just so with the growing 
piece of cartilage. When it is so shifted that its growing 
circumferential part is brought into view, the corpuscles 
can be observed gradually to become smaller and less 
perfect as they approach the margin; therefore giving in 
this respect the same evidence of coalescence as the 
globules of carbonate on the slide, on which the larger are 
known to be formed by the union of the smaller. Besides, 
if the growing circumferential part of this piece of car- 
tilage had increased by the addition only of cells dividing 
each into two, and these again, after having attained a 
state of maturity, dividing each into two more, and so on, 
the margin of the cartilage ought to give much better 
indications of the fact than the central portion, whereas 
the reverse is the case, the margin presenting nothing but 
small, incomplete, and irregularly shaped particles. The 
growth of cartilage, as here described, can be very well 
seen in the extreme phalanges of the toes of a frog whilst 
in progress of development from the tadpole-condition. 
But cartilage, being made up of particles, sometimes not 
very dissimilar to those of the surrounding parts, is not so 
well calculated to give positive evidence either in favour of 
one or the other view of development, as some other soft 
structures—as, for example, the branched pigment-cor- 
puscles. I have chosen these corpuscles for examination, 
these being formed by the aggregation of opaque black 
particles, can be distinguished in a very early stage, and 
when their size is very small; corresponding in this respect 
with the calcareous particles of shell and bone. The 
accompanying plate (see fig. 9) 1s an accurate representa- 
tion of these so-called cells, as seen in the periosteum of 
the fang of a tooth taken from a foetal calf. In this 
