HETEROMORPHOSIS 149 
incision b, while none have grown from the incision c near 
the foot end, even though the lips of the wound were pre- 
vented from healing together. In the drawing which was 
made from life, the cut is relatively far removed from the 
foot end of the animal. This is because the aboral end cd 
lying behind the second cut is greatly stretched, while that 
portion of the animal lying anterior to the incision is con- 
tracted. It will also be seen that after such an incision both 
parts become independent of each other to a certain extent, 
much as after transverse section of the spinal cord in one of 
the higher animals the incision renders the two parts of the 
animal comparatively independent. 
3. I found nostatement in the literature as to whether or 
not such observations had already been made upon other 
animals. It is, however, known that a new Hydra may spring 
from the body of an old one, which increases in size, and 
after a certain time separates from the mother to lead an 
individual existence. As long as it remains attached to the 
mother, the whole is to be regarded as an animal with two 
heads situated one above the other; for the body cavities of 
the young and the old animal communicate with each 
other. Yet such a Hydra is essentially different from our 
Cerianthus. While in Hydra not only a head, but a whole 
body is formed, only the oral plate is formed in Cerianthus. 
While the new animal becomes detached after some time in 
Hydra, the new head in Cerianthus remains permanently 
attached to the mother. Furthermore, while in Hydra the 
newly formed individual has the same number of tentacles, 
and the same cylindrical form as the mother, the number of 
tentacles that grow in Cerianthus is dependent upon the size 
of the incision. The smaller the incision, the smaller is the 
number of tentacles that are formed. Only a segment of a 
head, corresponding to the size of the incision, is therefore 
formed when an incision is made into a Cerianthus. A 
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