Influence of the Nervous System 713 
The following experiments that | made on Dendroccelum lac- 
teum may throw some light on this question: 
Experiment 1. Section at level a of Fig. 22 leaves the anterior 
piece presumably without cephalic ganglia. Such pieces died 
within a few ays. 
Experiment 2. Section through the cephalic ganglia. The 
anterior piece usually dies in a few days. Survivors do not regen- 
erate posteriorly. In one such piece a heteromorphic head was 
regenerated. 
Experiment 3. Section through b or any level anterior to 
X. Posterior pieces regenerate a head, anterior pieces a 
tail. If a cut be made through any level posterior to X the 
anterior piece regenerates a tail, but the posterior piece does not 
regenerate a head. X is the imaginary line that marks the level 
posterior to which no head is regenerated. In one case however 
the posterior piece cut just beyond the anterior end of the pharynx 
regenerated a heteromorphic tail. On the view previously men- 
tioned, the absence of cephalic ganglia and that portion of the two 
cords anterior to X and marked ¢’ and ¢, is responsible for the lack 
of formation of the head. This view was tested by the following 
experiments. | 
Experiment 4. The animals were cut along the line d, removing 
ganglia and a part of the cord c, anterior to X._ Both pieces com- 
plete themselves to form two typical animals. 
Experiment 5. If d vided at e, the posterior piece contains a 
small portion of the region anterior to X, but without the cords 
or c’, or the ganglia. No anterior regeneration took place: 
Experiment 6. If the cut be made through f or g the posterior 
piece like the preceding contains neither ganglia nor cord ¢ and ¢’. 
It contains mbre tissue anterior to X. Under these circumstances 
the projecting piece often sloughs off or shrinks down to a more 
posterior level and, like those planaria in Experiment 5, produced 
no head. When little or no sloughing takes place a head is 
regenerated, which may be complete and ultimately typical, or 
incomplete. It would appear as though more incomplete heads 
tended to appear on the longer strips, though [ cannot be certain 
about this. 
