110 Victor E. Emmel. 
PAGE. 
VIII. Directionvof differentiation” 22-45...-7520e eee ee eee 146 
1. Chitinogenous plates or muscle tendons ..................- 147 
2. Myoibrillse: +20..cire aooitasiteatier eta notre Hee eee 150 
3. striation of muscesibrilsye-ee ere eestor eee eee 151 
4. ‘Conclusions. .iscc4 025, foe enien tee ee ee eee 151 
PX.” -SUMMALY’ esis crectials SEs Slee eyotere Sse ree eee ern aero eee 152 
RR. Diteratures sa vic Halos v ors ererever the eanteee nie cess ial ore eee 155 
<I. ~Description of plates i522. cascicetern tec ie «sie he clot onic one ee 157 
INTRODUCTION. 
The recent work by Reed ((04) on regeneration in the crayfish, 
Ost ((06) on Oniscus, and Steele (’08) on the regeneration of the. 
compound crustacean eye, draws attention to certain fundamental 
questions. Their results are in marked contrast with the observa- 
tions made on vertebrates where it appears that a regenerating tissue 
almost invariably arises from similar pre-existing tissue. The im- 
portant relations of this subject to the problem of both the normal 
and pathological origin and cytomorphosis? of new tissue cells, render 
it desirable to investigate further the histogenesis of regenerating 
tissues. The present paper contains the results of a cytological 
study of the cells and tissues in the regenerating chela of the lobster, 
a crustacean which has been especially favorable for this study, both 
on account of its highly developed capacity for regeneration and 
because of the unsurpassed opportunity for obtaining suitable mate- 
rial at the lobster hatcheries. 
The results to be described deal more especially with (1) the eyto- 
logical changes observed in the regenerating ectodermal cells; (2) 
the genesis of striated muscle, nerve, and connective tissue; and (3) 
the morphology of certain structures at the breaking joint of the limb, 
which as far as the writer is aware, has not previously been con- 
sidered. 
I desire to express my thanks to Professor C. S. Minot, of the 
Harvard Medical School, for interest and encouragement during the 
*This term is used “to designate comprehensively all the structural modifica- 
tions which cells or successive generations of cells may undergo, from the 
earliest undifferentiated stage to their final destruction.” See Minot (’01, 
p. 494.) 
