REGENERATION AFTER EXARTICULATION AT, 
on at the same time and as far as possible treated in the same 
manner, some always healed more readily than others. Re- 
garding temperature—the higher degrees were in general more 
favorable to rapid regeneration than the lower as might be ex- 
pected, but there was so much individual variation due to time 
of healing that no great reliance can be placed on this statement. 
Comparing, from the standpoint of time, regeneration after 
exarticulation with regeneration after wounding a bone, one finds 
that the former is appreciably slower. On the average, there is 
about ten days difference in corresponding stages. 
With regard to regeneration of soft parts (muscle, nerve, blood- 
vessels, etcetera), there is nothing to add to the accounts already 
published. Muscle regeneration has been very carefully worked 
out by Towle (01) in Plethodon and Schminke (’07) in Triton 
taeniatus and T. ecristatus. These writers agree that the new 
muscle is formed chiefly by isolated cells (sarcoplasts) which 
arise from degeneration of the old muscle of the stump. The 
sarcoplasts are small masses of cytoplasm which contain at first 
several nuclei. They usually break up into small cells which 
are responsible according to Towle (01) for the accumulation 
of nuclei (cells) in the growing bud distal to the stump of the 
old bone where they give rise to new muscle fibers. It was 
previously mentioned that the exact origin of this entire mass of 
small cells is somewhat uncertain (cf. Wendelstadt). Probably 
most of the cells originate from degenerating muscle and some 
perhaps from other soft tissues. In any event, there is no evi- 
dence that any are derived from bone or cartilage. Histologically 
there is: at first no sign of differentiation in these cells, and it 
seems useless to assume that such exists. It is from a part of 
them, however, that new embryonal cartilage is developed in 
the midst of the bud. This seems to be an example of dediffer- 
entiation followed by redifferentiation in the sense of Child (15). 
From the apparently indifferent mass both cartilage and muscle 
are formed, the cartilage showing the typical embryonic type of 
development. 
A somewhat similar process is to be seen in the behavior of the 
old epiphyseal cartilage of the femur. Here the matrix breaks 
