HYDRJD,< OR FRESH-WATER POLYPES. 277 
without a new body. If only two or three tentacula are 
embraced in the section, the result is the same ; and a single 
tentaculum 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 unscarred parts ; when a polype is introduced 
by the tail into another's body, the two unite and form one 
individual ; and when a head is lopped off, it may safely be in- 
grafted on the body of any other which may chance to want 
one. You may slit the animal up, and lay it out flat like a 
membrane, with impunity ; nay, it may be turned inside out, 
so that the stomachal surface shall become the epidermous, 
and yet continue to live and enjoy itself. And the animal 
suffers very little by these apparently cruel operations — 
Scarce seems to feel, or know 
His wound — • 
for before the lapse of many minutes, the upper half of a cross 
section will expand its tentacula and catch prey as usual ; and 
the two portions of a longitudinal division will, after an hour 
or t^wo, take food and retain it. A polype cut transversely 
in three parts, requires four or five days in summer, and longer 
in cold weather, for the middle piece to produce a head and 
tail, and the tail part to get a body and head, which they both 
do in pretty much the same time/' Although no one who has 
examined Trembley's celebrated Memoir can doubt the general 
truthfulness of his observations, it is very desirable that further 
experiments should be made, with a view to verify his state- 
ments. There is need of much patient investigation before 
every thing Trembley has written on the nature of the hydra 
can be, or ought to be, finally accepted. It is too much the 
habit of zoologists to take for granted the conclusions of pre- 
vious observers. I fully believe, from experiments I have 
made upon the hydrae, that Trembley's account is wondrously 
accurate ; but there are certain points in the physiology of these 
animals — as for instance, that one of their being able to 
assimilate their food when their bodies are turned inside out 
— that demand further investigation. 
