HETEROMORPHOSIS 129 
which Allman and Dalyell experimented, behaves typically 
differently from Tubularia mesembryanthemum, upon which 
I made my experiments. <A certain difference seems, in- 
deed, to exist. Dalyell states that the stem of the Tubularia 
indivisa bends upward, when laid horizontally; this I have 
not observed in Tubularia mesembryanthemum. 
Yet I do not believe that the conditions determining the 
form of Tubularia indivisa differ in principle from those in 
Tubularia mesembryanthemum. For Dalyell notes that he 
once observed the growth of polyps from both ends of a 
piece cut from the middle of a Tubularia indivisa. “It 
may be conjectured that the summit of both had originally 
constituted a single embryo, which by partition developed 
into two, becoming progressively symmetrical in maturity.”” 
To explain the formation of a head at both ends of the 
stem in the single case just described, Dalyell therefore 
assumes that the new head divided in the course of its 
development. Such a division would, in consequence, always 
have to occur in the case of Tubularia mesembryanthemum, 
which without exception forms a head at both ends, if both 
ends are surrounded by water and have a sufficiently great 
diameter, and a dividing embryo would therefore have to 
exist in every piece of the stem of Tubularia mesem- 
bryanthemum. Even if one were willing to consider this 
hypothesis, it yet could not be made to harmonize with 
Allman’s theory of polarity; for, according to this theory, 
both embryos would necessarily have to develop always 
at the same end, namely, at the oral one; yet I have never 
found two heads to develop here side by side. 
2. I might mention that it is possible apparently to ob- 
tain such results in Tubularia mesembryanthemum as All- 
man describes, if the stems used in the experiments are cut 
off close to the root, and if care is taken, in choosing the 
1 Loc, cit., p. 35. 
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