Tissues in the Crustacean Limb. 135 
muscle fiber and become more spherical in form (Figs. 16, 22, 24, 
and 25). These nuclei now seem somewhat larger than the earler 
ectodermal nuclei, an appearance which may be partly due to the 
change from an elongated to a rounded shape. The chromatin ap- 
pears coarsely granular and has a fairly even distribution, the nucleus 
as a whole taking a lighter stain. In later differentiation the nuclei 
again become flattened and considerably elongated in the direction 
of the long axis of the muscle fiber. The present observation indi- 
cates that the more peripheral of these nuclei eventually become the 
nuclei of the sarcolemma, but more evidence is necessary to establish 
this point. 
In the formation of muscle fibers from a syncytium of ectodermal 
cells, each fiber is from the very first multinucleated. Instead of 
“each muscle bundle developing from a single cell” (Claus, ’86, p. 
33), as seems to be the case in the normal development in Branchipus, 
for example, each bundle is multicellular in origin. Furthermore, 
the nuclei increase in number, with the growth of the fiber, by mitotic 
division, the spindle frequently occurring at right angles to the long 
axis of the fiber. Consequently in regard to the discussed question 
of direct and indirect division of muscle nuélei, it is evident that in 
the regenerating muscle of the lobster at least, mitotic division per- 
sists even after the differentiation of myofibrille has advanced to a 
considerable degree. 
The conclusion that regenerating striated muscle is ectodermal in 
origin, draws attention to the problem of the genetic relationship 
of tissues and the primary germ layers, the question at issue being 
whether in regeneration a given tissue arises from the same germ 
layer as in normal development. An adequate discussion of this 
question in the case of the crustacean muscle, involves, of course, 
an accurate knowledge of the histogenesis of the tissue under con- 
sideration, in both the regenerative and ontogenetic processes. 
With regard to regeneration, as a result of the work of Reed 
(704) on the oerayfish, Ost (’06) on Oniscus, and the present study 
of the lobster, we have at hand a fairly exact mass of data concern- 
ing the genesis of the regenerating crustacean muscle, but as for its 
origin during normal ontogeny, the evidence does not appear suffi- 
