146 Victor E. Emmel. 
As to the origin of the regenerating ‘‘Grenzlamelle,” the present 
observations fail to furnish conclusive evidence. The fact, how- 
ever, that the regenerating bud becomes filled with ectodermal cells 
involved in the regeneration of muscles and nerves, and the lack of 
clear evidence of cell proliferation from the old connective tissue, 
suggests an ectodermal origin. Of interest in this connection are 
Claus’s observations on the normal development of Branchipus :— 
“Was man als solche (connective tissue) beim ersten Blick in An- 
spruch zu nehmen geneigt ist, erweist sich wenigstens an vielen 
Stellen nach genauer Betrachtung als eine Art innere Cuticula, die 
aus der Basis des Epithels durch Erhartung des Protoplasmus ent- 
standen ist” (p. 21). On the other hand, Schneider (’02) from a 
comparative point of view is unable to support this conclusion: “Nach 
Claus stammen die Grenzlamellen und die Muskelsehnen mindestens 
zum Teil vom Epiderm, dessen Deckzellen die basalen ausscheiden 
sollen. Dieser Ansicht kann in Riicksicht auf die Verhialtnisse bei 
anderen Arthropoden, wo die Sehnen und Lamellen unzweifelhaft 
Bindegewebsbildungen sind, nicht beigestimmt werden, wenn auch 
die Bildung von Seiten des Bindegewebes nicht bekannt ist” (p. 
466). 
VIII. Tue Direction or DIFFERENTIATION. 
The question of the direction in which the process of differentia- 
tion proceeds in both regeneration and normal ontogeny is a subject 
which has given rise to diverse opinions. In elaborating certain 
theories of form regulation, Holmes (’04) assumed that in a regen- 
erating appendage, differentiation proceeds from the base toward 
the tip, whereas Child, at least in an earlier paper (’06), was in- 
clined to regard the reverse as generally true.’?. Zeleny (’07) found 
in the regenerating antennule of Mancasellus that there are two 
distinct periods of development, in the first of which the process of 
differentiation “begins at the base and travels irregularly outward”, 
while in the second period, the process is in the reverse order, 2. ¢., 
beginning with the terminal segment and differentiating inwards (p. 
"Holmes (’07) and Child (’08) have later restated their theories as not 
being inconsistent with differentiation in either direction. 
