E. Hindle and N. Cunlipfe 
369 
Discussion. 
It seems impossible to explain the above-described results on 
Muller’s theory that when regeneration takes place the new portion 
takes on an atavistic form. This theory was based on his observation 
(Fritz Muller, 1880) that when the chelae of the Brazilian shrimp, 
Atyoida potimirim, a long clawed form, were amputated, the regenerated 
limb reverted to the short clawed type of the related genus Garidina, 
the latter genus being phylogenetically older than Atyoida. 
Similarly Giard (1897) and Bondage (1897-1900) noted that when 
the tarsus of a pentamerous insect was removed, it regenerated a 
tetramerous appendage. They considered this as a reversion to the 
type of limb in the primitive Apterygota, in which group tetramery is 
found. Bordage, however, in his paper on the tetrameric regeneration 
of the tarsus of the Phasmidae, noticed that sometimes a five-jointed 
tarsus was regenerated. Similar results were also obtained by Brindley 
(1897) in the case of the Blattidae. These results might be explained 
on tbe supposition that the power of regeneration was imperfectly 
developed, and that the four-jointed tarsi were merely examples of 
incomplete regeneration. Barfurth, however, showed that when the 
four-toed anterior appendage of an Axolotl was amputated an atavistic 
five-toed appendage was regenerated. 
On the whole we think our results could be best explained by 
adopting Bonnet’s idea of specific substances flowing in definite 
directions. The hypothesis with some modifications has been applied 
by Sachs and also Goebel to explain regeneration in plants, and both 
Loeb and Driesch have also used the same idea to explain the regenera¬ 
tion of Tubularia. In this polyp there is present in the hydranth and 
stem a red pigment in the form of granules in the endodermal cells. 
This pigment is concentrated in that part of the stem adjoining the 
hydranth. If a piece of the stem is cut off, it closes its cut ends and 
in the central cavity a circulation of fluid begins. Globules containing 
the red pigment granules now appear in this fluid. In the course of 
twenty hours the new hydranth begins to appear near one end of the 
stem and in this region the granules are reconcentrated, disappearing 
from the circulation. 
Similarly, we suppose that formative substances are contained in 
the body of the tick. During the period of growth these substances 
are continually being distributed to their specific localities in the body. 
