REVIEWS OF RECENT LITERATURE. 123 
well known that in tadpoles, especially, nearly all the cells are 
heavily laden with yolk granules until a relatively late period of 
development. Of this the author takes no account. It is quite 
conceivable that local growth might take place without any general 
or local increase in the percentage of water. Until the larva is 
able to take food the increase in the dry weight of the living 
material is due to assimilation of yolk, and it may be that local 
growth during this period is due solely to the solution, transference, 
and assimilation of this food supply stored within the organism. If 
it can be shown that there is an increase in the percentage of water 
in a local growth, such, for example, as a gill-bar, it may well be that 
it is a purely secondary phenomenon. Then the question, What 
determines excessive local growths? would not resolve itself into, 
What determines excessive local imbibition of water? but into, 
What determines excessive transference and assimilation of yolk 
material? In supposing that local growth is due primarily to the 
absorption of water, whether active or passive, we are assuming a 
simplicity of operation that is hardly warranted by the known com- 
plexity of living material. 
The paper is well illustrated by tables and plotted curves. 
The Capacity for Regulation in the Development of Organisms. 
— The word “regulation,” as employed by Driesch, expresses the 
capacity of an organism to obliterate in development the effects of 
any malforming influence to which it has been subjected, so that, 
despite the mutilation, it develops into the normal form. Driesch’s 
former studies had been chiefly made upon developing eggs; he now 
(Arch. f. Entwicklungsmech. Bd. v, Heft 3, 1897) examines some 
cases of regeneration. 
As is known from the studies of Miss Bickford, regenerating 
stems of Tubularia do not form new tentacles by a sprouting out at 
the cut edge, but by a metamorphosis of the old tissue of the stem 
just below the cuj. The old tissue thickens along a number of longi- 
tudinally lying areas, representing the future tentacles, which soon 
become fully formed. This phenomenon of differentiation in place 
is called by Driesch reparation. The first question Driesch asks is: 
If the repairing stem be split lengthwise so that a double head is 
formed, will the normal number of tentacles be repaired through 
regulation on each half head? The result showed that nearly or 
quite the normal number is so formed. 
Again, if the head is cut off and regenerated, and then cut off a 
second time, will the time elapsing before complete reformation be 
