No. 420.] REGENERATION IN THE EGG. 951 
completely replaced the lost smaller part. It may also be stated 
that the result is not dependent upon a lack of material in the 
small piece, for the process of regeneration does not even begin, 
and, as other experiments have shown, there is certainly enough 
material in the small piece for regeneration to have been carried 
out to some considerable extent. 
b. The other case in this category is that in which the large 
piece produces only the distal end of the part removed and, 
therefore, less than the part cut off. For instance, if more 
than five segments are taken from the anterior end of the 
earthworm, still only five are regenerated, and the intermediate 
region is never regained. In the planarian, if more than the 
head is cut off, only the head is aż first regenerated, but in this 
case the intermediate, or missing region, is made good by sub- 
sequent changes that take place in the region behind the new 
head and in front of the old part. A similar thing happens 
when the posterior end is cut from an earthworm. At first 
only a small part comes back, consisting of the end-piece — the 
telson — and a few segments, but by subsequent growth td 
segments are intercalated near the posterior end just in front 
of the telson. Again, if the tail of a fish is cut off near its 
base, there appears at first only a small new par t that assumes 
the characteristic form of the tail, even before the new part has 
the tail was cut off. Subse- 
grown out to the level at which ud 
quently, by a process of continuous growth, the entire 
replaced. ; eid. 
(B) a. The second mode in which the process o ge m 
tion takes place is, as I have said, by the transformation 
entire piece into a new organism. 
The most familiar case, and the one longest known, serit 
hydra. Trembley saw that small pieces Se ved viis 
whole animals, and subsequent investigators have mms cifically 
same thing. They have not, however cune quisque 
that new tissue is not added at the cut-ends, but from pe 
Observation I can state that there is 
new tissue in these regions. The 
no special development of 
entire piece changes over 
