132 Victor E. Emmel. | 
lack of evidence of cell division in the connective tissue, and (2) 
the fact that at no stage of development did there appear to be a 
migration of connective tissue cells into the regenerating bud. 
In a word, the results of these observations lead to the unexpected 
conclusion that certainly the greater part, and probably the entire 
mass, of cells composing the interior as well as the wall of the regen- 
erating limb bud, are ectodermal in origin. 
VIL. Tur DirFERENTIATION OF TISSUES. 
1. Striated Muscle—a. Histogenesis.—The first differentiation ~ 
of striated muscle, as indicated by the formation of myofibrillee, 
became apparent as early as five days and twenty-two hours after 
amputation. On the sixth day the fibrillee were readily distinguished. 
At the center of a longitudinal section through the second segment or 
propodite (Fig. 16, six days, six hours) may be seen the tongue of 
ectodermal cells invaginated for the flexor muscle of the dactyl. The 
space between the epidermal cells (e) of the regenerating exoskele- 
ton, seen at the lower side of the figure, and the invagination, 1s filled 
by a mass of cells, the ectodermal origin of which has already been 
considered. It is within this central mass of cells that the myofibrillee 
(mf) first appear. These fibrillee, instead of extending as straight 
fibers between their origin in the invagination and their insertion in 
the epidermal wall, are considerably curved, being convex in a proxi- 
mal direction. This curvature of the myofibrils does not entirely 
disappear until after the moult of the lobster has occurred and the 
regenerated limb has become functional. It may be justly questioned 
whether there is any correlation between the appearance of these fibrils 
and functional activity, such, for example, as Eycleshymer (’05) 
describes in the Necturus embryo, for there is no evidence of func- 
tional activity in the regenerated limb until it has been liberated 
from its enveloping membrane during moulting. 
The cytoplasm in which the myofibrils are first seen to differentiate 
(Fig. 22) appears finely granular in structure and is traversed by a 
delicate cytoplasmic reticulum (7t). As soon as the fibrillee can be 
distinguished from the cyto-reticulum they appear as heavier fibers 
