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 1 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." 2 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 Las 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. XXXVII (1882). 



2 M. NUSSBAUM, Archivfiir mikroscopische Anatomic, Vols. XXVI and XXIX. 



