808 
ROSS GRANVILLE HARRISON 
isolated cells of various idnds have been well preserved (fig. 12) 
but satisfactory preparations of the nerve fibers have not been 
obtained. Some of the preparations have been cut into serial 
sections. Nerve fibers were found within them, but in all cases 
they were broken off at the surface of the tissue. 
This defect in method has in a measure been offset by the experi- 
ments described elsewhere ('10) in which the nerve fibers from the 
medulla oblongata were shown to have grown into a blood clot 
implanted in their path. 
General description of material 
The developmental processes which have been observed in speci- 
mens prepared as described in the last section involve only the 
histological differentiation of the tissues. The gross morpholog- 
ical changes have no resemblance to those which take place within 
the embryonic bod3^ This is as might be expected even on purely 
mechanical grounds, for the stresses and strains which are brought 
to bear upon the developing organs when enveloped in the fibrin 
must be entirely different from those within the intact embryo. 
From the time when the tissue is implanted in the lymph it 
shows a tendency to spread out (fig. 16), and often broad laminae 
made up of a single layer of cells {I) are found at the periphery of the 
mass, while individual cells may move off entirely by themselves. 
This is the case with both nervous and axial mesodermic tissue, as 
well as with pieces of ectoderm, though the latter more often roll 
themselves into complete spheres. One notable peculiarity that 
has frequently been observed is the formation of large round 
or oval openings in the flattened tissue {fen), which may be sur- 
rounded by very narrow bands or rings of tissue with cells some- 
times in single file {cd). This phenomenon may possibly be due 
to the mechanical action of the fibrin upon the implanted tissue, 
but the spreading out of the cells into thin sheets seems to result 
largely from the activities of the cells themselves. These activi- 
ties, which are common to several tissues, in fact to all except 
the -very inert yolk-laden endoderm and, perhaps, the notochord, 
may be referred to a form of protoplasmic moyemcnt having its 
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