INO. 3) ] TUBULARIAN HYDROIDS. 423 
are by no means as absolutely fixed and unchangeable as some 
of the modern ideas of heredity make it appear. 
The next stage in the regenerative process is shown in 
Fig. 5. After the formation of the tentacles, with their central 
axes of richly pigmented cells, the hydranth emerges from the 
perisarc, and from this time on the growth of the stems in 
length is quite rapid, in some cases as much as 7 mm. in 
six days. 
(c) Another experiment, showing that the complete hydranth 
is formed within the perisarc, was performed as follows:—A 
large stem attracted special attention by the arrangement of the 
pigmented bands, which appeared rather farther apart than 
usual. In order to study this more fully, ten sections of the 
stem were made, one below each pigmented row (see Fig. 
A,xandy). The contents of each piece were carefully pressed 
out of the perisare containing it. 
The first piece was found to be an irregular mass, with a 
fringe of very short tentacles around one side (see Fig. 7). 
Shortly after it was pressed out, the cut ends closed in, and it 
assumed a more hydranth-like form (see Fig. 8). The second 
fragment was then examined and appeared somewhat hydranth- 
shaped, with a large proboscis portion, surrounded by a row 
of long tentacles, which were in slow motion (see Fig. 10). 
Evidently the first cut had been made between the regions of 
the oral and coronal tentacles, dividing the hydranths into two 
parts. These fragments were placed in fresh sea water until 
the next morning, when they were again examined. The first 
portion had become definitely hydranth-shaped, and the tenta- 
cles had increased in length (see Fig. 9). The second fragment 
had also changed (Fig. 11), the proboscis was still much larger 
than in the normal hydranths. This form was also in very 
active motion. The next day both fragments were dead. 
III. REGENERATION OF TRANSVERSE SECTIONS OF TUBULARIA. 
(a) While studying the process of regeneration a small stem 
about 3 mm. in length was found, on which was the old 
hydranth, not completely severed, yet alive, and a new 
