716 A. Ff. Goldfarb 
removal of the cerebral ganglia and that part of the cords called ¢ 
and c’ inhibits anterior but not posterior regeneration. Further- 
more, removal of the cerebral ganglia and the cord on one side, or 
the removal of the ganglia and the cord anterior to X, Experiment 
13, does not prevent lateral regeneration. Yet if I mm. or per- 
haps a fraction of a millimeter more of the cord be removed, 
lateral growth is prevented. 
Experiment 15. The mechanical interference of parts men- 
tioned in Experiment 8 is also shown, where one might least 
expect to find it, viz: in the posterior part of the body. A long 
central strip 7, including both cords, was removed from the tail 
(Fig. 23). The two remaining flaps came together. If these 
sloughed off regeneration took place from the more anterior end. 
When sloughing did not take place the two strips remained firmly 
united, preventing in the great majority of the planaria any lateral 
regeneration of tissue between the strips. 
Summary 
It is improbable that the removal of the nervous system in the 
anterior third of the planarian D. lacteum is responsible for the 
lack of regeneration of a head in posterior pieces, because, 
1 The removal of this part of the nervous system does not pre- 
vent regeneration of a tail; 
2 The presence of only one-half of this portion of the nervous 
system sufhces to permit regeneration of a head and lateral half 
of the animal; 
3 It was further shown that a fraction of one of the cords suffices 
for the regeneration of a head; 
4 Finally, regeneration of a head took place when the whole of 
the cerebral ganglion and cords c and c’ were cut away. 
The essential condition in the above categories seems to be the 
presence of a sufhcient quantity of body tissues anterior to X. 
The latent power to replace missing parts may be checked by 
means other than the removal of the nervous system, namely, by 
the “mechanical interference of the parts.” In this way both 
anterior and posterior regeneration can be prevented. (Experi- 
ments 8, 10, 15.) 
