694 CLARENCE L. TURNER 
nificant that germ cells in embryos generally do not divide while 
they are migrating. 
Once the germ cells have become lodged they undergo an im- 
mediate change. A comparison of a and 6 in figure 3 indicates 
that there is a slight increase in volume. There is also the for- 
mation of some darkly staining spherules which accumulate 
around the nuclear wall and pass out into the cytoplasm (fig. 
33). The actual formation and extrusion of these spherules is, 
of course, a matter of interpretation, but no spherules are found 
in the nucleus of the migrating cells except the plasmosome, and 
the cytoplasm is entirely free from them. Such a change might 
well be brought about by a change in the metabolism of the cell. 
During migration the energy would be consumed in locomotion, — 
but when the cell becomes sedentary the energy would be di- 
verted into growth and a reorganization of the cell contents 
preparatory to division. 
There is a striking parallel between the behavior of the germ 
cells in the adult perch and the embryonic cells described for 
Lophius by Dodds (710). He remarks as follows: 
In all vertebrates examined, this period (of growth) corresponds to 
the time during which the germ cells are in active migration, and it 
has been suggested that possibly the energy of the cell is expended in 
locomotion rather than in growth and cell division. 
The above discussion of conditions observed in these cells during the 
rest period offers no explanation why this period of suspended activity 
begins, nor why after a time it comes to an end. At its beginning, 
before there are any differences we can detect with the eye, there must 
be an unseen physiological difference which determines the future be- 
havior of the cell. Whatever the nature of the difference, it is one of 
the earliest of which we have evidence in the cleaving egg of Lophius. 
The migration occurring in the perch seems to correspond to 
the period of rest. Dodds has also called attention to the fact 
that the germ cell retains its embryonic character longer than 
any of the other tissues of the body. It is possible that the germ 
cells migrate seasonally because they have not differentiated, 
even in the adult perch, and that they are only fulfilling their 
innate tendency to migrate whenever the opportunity offers or . 
when there is a proper stimulus provided. The problem en- 
