HETEROMORPHOSIS 117 
the opposite end. That Allman chose the name “polarity” 
for this behavior suggests the possibility that he may have 
thought of the analogy of this fact to the behavior of a mag- 
net; for a fragment of a broken magnet always has a north 
pole at that end which in the original magnet was directed 
toward the North Pole. If however, the book of Dalyell is 
subjected to a close scrutiny, it is found that this author 
occasionally (at two or three places in the book) mentions 
observations which do not harmonize with the theory of 
polarity. In these cases, however, Dalyell believed that he 
was dealing with accidental monstrosities which this careful 
and patient observer did not consider of sufficient impor- 
tance to follow out experimentally, or to take into considera- 
tion for a theory of organization. 
W. Marshall’ builds on Allman’s theory of polarity in 
his experiments upon Hydra. When Hydra vulgaris is cut 
into pieces, ‘‘one is struck most forcibly with the extraordi- 
nary polarity of the animal, in consequence of which new 
tentacles and a new mouth are always formed at the oral 
edge of the cut piece” (p. 698). 
A further expression of this idea is found in Nussbaum’s 
papers on “The Divisibility of Living Matter.”’ Nussbaum 
found that when a piece is cut from an Infusorian, new cilia 
develop from the edge of the wound in the same number 
and in the same position that they occupied before the 
injury. He goes even farther than Allman and concludes that 
Every minute particle of living protoplasm is oriented; otherwise 
we could not understand the regular appearance of new cilia at 
definite points when the infusorian has been divided. Just as we 
can distinguish in an infusorian between the anterior and the pos- 
terior, right and left, and dorsal and ventral surfaces, so each 
minute particle of protoplasm must likewise be oriented according 
to the three axes in space. 
1W. MARSHALL, Zeitschrift fiir wissenschaftliche Zoologie, Vol. XXXVITI (1882). 
2M. NusspauM, Archiv fir mikroscopische Anatomie, Vols. XXVI and XXIX. 
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