29 
depends largely on the supply of fo.d and on temperature. If a 
rapidly budding Hydra be transferred to water in which there is 
little ur no food to be obtained, the formation of buds will be 
stopped, and those already formed may even be absorbed. A single 
Hydra may develop more than one bud at once, and these may 
develop secondary buds before separating from the parent animal. 
In this way temporary colonies may be formed, which however, 
sooner or later, break up into their component units. 
Hydra can also multiply by fission, i.e., it can be cut in two, 
and each half will become a perfect animal. The process of fission, 
however, very rarely occurs naturally. 
On this subject Johnston on “ British Zoophytes ” writes :—“ If 
the body is halved in any direction each half in a short time grows 
a perfect hydra ; if it is cut into four or eight or even minced up. 
into forty pieces each continues alive and develops a new animal, 
which is itself capable of being multiplied in the same extra- 
ordinary manner. If the section is made lengthwise, so as to 
divide the body into two or more slips, merely connected by the- 
tail, they are speedily resoldered like some heroes of fairy tale, into 
one perfect whole; or if the pieces are kept asunder each will be- 
- come a polyp: and thus we may have two or several polypes with 
only one tail between them, but if the section be made in a contrary 
direction from tail towards the tentacles, you produce a monster 
with two or more bodies and only one head. If the tentacles—the 
organs by which they take their prey, on which their existence 
might seem to depend—are cut away, they are reproduced, and the 
lopt off parts do not remain long without a new body. 
‘*« Tf only two or three tentacles are embraced in the section, the. 
result is the same, and a single tentacle will serve for the evolution . 
of a complete creature. When a piece is cut out of the body, the 
wound speedily heals, and as if excited by the stimulus of the 
knife, young polypes sprout from the wound more abundantly, 
and in preference to the unscarred parts; when a polype is in- 
troduced by the tail into another’s body the two unite and form 
one individual ; and when a head is lopt off it may be safely 
engrafted on the body of any other which may chance to want 
one.... And the creature even suffers very little by these 
apparently cruel operations. 
‘«« Scarce seems to feel, or know 
** His wound, 
_ “for before the lapse of two minutes, the upper half of a cross 
section will expand its tentacles and catch prey as usual ; and the 
two portions of a longitudinal division will after an hour or two 
take food and retain it.”’ 
I have omitted one sentence from the extract, as I have already 
alluded to it as discussed and disproved by modern scientists, 
