788 The American Naturalist. [September, 
the trunk segments of pantapods, and the body of ascidians. 
It became clearer that regeneration may proceed along very 
different lines from normal ontogeny— Wolff found the crystal- 
line lens regenerating from the edge of the iris instead of the 
outer skin. Girard found that well-fed and much exercised 
tritons regenerate polydactylic feét. 
Concerning the cause of regeneration, Nussbaum concluded 
that both regeneration and heteromorphosis depend upon in- 
different cells in the body; Loeb suggested that regeneration 
depends upon special organogenic substances (Sachs); and 
Rauber compared in much detail organic regeneration to that 
of a crystal and believed a causal relation to lie behind the 
similar phenomena. 
Grafting—This year will be remembered as that in which 
Born published the results of his marvelous experiments on 
uniting bits of tadpoles belonging even to different families. 
Important also are the experiments of Wetzel who obtained 
from his grafts of hydra additional evidence for the polarity 
theory. 
Polymorphism, metamorphosis and alternation of generations.— 
Advance was made (1) in the interpretation of many varieties 
as polymorphic forms; (2) in the determination of polymor- 
phic forms by external conditions, and (3) in the discovery of 
a hidden alternation of generations in organisms. For the 
first, Coutagne showed for molluscs and Standfuss for mosses — 
that similar varieties, due to the same causes, recur so fre- 
quently in different species that a few suffixes applied to the 
different specific names will suffice to designate all varieties. - 
As for the second, Dietel showed that, in the Uredineæ, the 
succession of aecidio-, uredo- and teleutospores may be varied 
at will; Wasmann got intermediate polymorphic forms in ants 
by intermediate food conditions, and Bachmann modified, by 
changing the character of the substratum, the form of the 
sporangia of Thamnidium. As for the third, the idea of Stras- 
burger (1894) was developed by others, so that the theory now 
seems well formulated that, as in the vascular cryptogams and 
the phanerogams, so also in all animals there is an alter- 
nation of generations, the sexual generation including the 
