418 BICKFORD. [Vou. IX. 
contact with a solid surface ;— on the other hand, the hydranths 
were produced on both ends of the stem when the water was 
allowed to play freely around thecut ends. To this phenomenon 
of the reproduction of an organ typically different from the 
one which had originally occupied that position, he has given 
the name heteromorphosis, and thus distinguishes it from the 
more usual phenomenon of regeneration through which a lost 
organ is replaced by one of the same kind. 
The experiments to be described in the following paper will 
serve to confirm and illustrate this principle of heteromorphosis ; 
—they will also deal with the regenerative power of Tubu- 
laria tenella, and with some of the regenerative processes. 
This work was suggested by Dr. Loeb, and was carried on 
at the Marine Biological Laboratory at Woods Holl. The 
hydroids were obtained from New Bedford, where they were 
found growing in great abundance during the early summer 
months. The size and transparency of the individual stems, 
also the fact that this form does not branch, rendered them 
especially suitable for such study ;——the last-mentioned char- 
acteristic aids in proving that the heteromorphosis of these 
forms is genuine, and does not depend upon any tendency to 
bud, as has been suggested by Trautzsch in opposition to 
Loeb’s conclusions. 
II. PrRocessES OF REGENERATION. 
(a) In order to give a clear conception of the changes which 
occur in the processes of regeneration, a brief sketch of 
the general anatomy and histology of hydroid structure 
gleaned from descriptions by Allman (1), Hamann (5), 
Jickeli (7), Ciamician (3) and others, will be presented here. 
The Tubularian hydroid consists of a stem portion, —the 
hydrocaulus, —terminating at the aboral end in a root-like 
expansion, — the hydrorhiza,—and at the oral end with the 
hydranth. This stem portion, which was the part chiefly used 
in these experiments, contains the fleshy tube-like axis known 
as the coenosarc, which is surrounded by an external horny 
layer, or covering, the perisarc. The coenosarc is mainly 
