HYDRA. 



size of a pea, and flatted upon one side. 

 The same kind of substances are likewise 

 to be met with on the under side of the 

 leaves of plants that grow in such places. 

 These are the polypes in a quiescent 

 state, and apparently inanimate. They 

 are generally fixed by one end to some 

 solid substance, with a large opening, 

 which is the mouth ; at the other, having 

 several arms fixed round it, projecting as 

 rays from the centre. They are slender, 

 pellucid, and capable of contracting 

 themselves into a very small compass, or 

 of extending to a considerable length. 

 The arms are capable of the same con- 

 traction and expansion as the body, and 

 with these they lay hold of minute worms 

 tnd insects, bringing them to the mouth, 

 and swallowing them. The indigestible 

 parts are again thrown out by the mouth. 

 The green polype was that first discover- 

 ed by M. Thembley : and the first appear- 

 ances of spontaneous motion were per- 

 ceived in its arms, which it can contract, 

 expand, and twist about in various direc- 

 tions. On the first appearance of danger 

 they contract to such a degree, that they 

 appear little longer than a grain of sand, 

 of a fine green colour, the arms disap- 

 pearing entirely. Soon afterwards, he 

 found the grisca,and afterwards the fusca. 

 The bodies of the viridis and grisca di- 

 minish almost insensibly from the ante- 

 rior to the posterior extremity ; but the 

 fusca is for the most part of an equal size, 

 for two-thirds of its length, from the an- 

 terior to the posterior extremities, from 

 which it becomes abruptly smaller, and 

 then continues of a regular size to the 

 end. These three kinds have at least six, 

 and at most twelve or thirteen arms. 

 They can contract themselves till their 

 bodies do not exceed on,e fourth of an 

 inch in length, and they can stop at any 

 intermediate degree of expansion or con- 

 traction. They are of various sizes, from 

 an inch to an inch and a half long. Their 

 arms are seldom longer than their bodies, 

 though some have them an inch, and 

 some even eight inches long. The thick- 

 ness of their bodies decreases as they 

 extend themselves, and vice versa ; and 

 they may be made to contract them- 

 selves, either by agitating the water in 

 which they are contained, or by touch- 

 ing the animals themselves. When taken 

 out of the water they all contract so much, 

 that they appear only like a little lump 

 of jelly. They can contract or expand 

 one arm, or any number of arms, inde- 

 pendently of the rest ; and they can like- 

 wise bend their bodies or arms in all 

 possible directions. They can also dilate 



or contract their bodies in various places, 

 and sometimes appear thick set with 

 folds, which, when carelessly viewed, ap- 

 pear like rings. Their progressive mo- 

 tion is performed by that power which 

 they have, of contracting and dilating 

 their bodies. When about to move, they 

 bend down their heads and arms, lay 

 hold by means of them on dome other 

 substance to which they design to fasten 

 themselves ; then they loosen their tail, 

 and draw it towards the head ; then 

 either fix it in that place, or stretching 

 forward their head as before, repeat the 

 same operation. They ascend or descend 

 at pleasure in this manner upon aquatic 

 plants, or upon the sides of the vessel in 

 which they are kept; they sometimes 

 hang by the tail from the surface of the 

 water, or sometimes by one of the arms ; 

 and they can walk with ease upon the 

 surface of the water. On examining the 

 tail with a microscope, a small part of it 

 will be found to be dry above the surface 

 of the water ; and, as it were, in a little 

 concave space, of which the tail forms 

 the bottom ; so that it seems to be sus- 

 pended on the surface of the water on the 

 same principle that a small pin or needle 

 is made to swim. When a polype, there- 

 fore, means to pass from the sides of the 

 glass to the surface of the water, it has 

 only to put that part out of the water by 

 which it is to be supported, and to give it 

 time to dry, which it always does upon 

 these occasions ; and they attach them- 

 selves so firmly by the tail to aquatic 

 plants, stones, &c. that they cannot be 

 easily disengaged : they often further 

 strengthen these attachments by means 

 of one or two of their arms, which serve 

 as a kind of anchors for fixing them to 

 the adjacent substances. 



The fusca has the longest arms, and 

 makes use of the most curious manoeuvres 

 to seize its prey. They are best viewed 

 in a glass seven or eight inches deep, 

 when their arms commonly hang down 

 to the bottom. When this or any otheF 

 kind is hungry, it spreads its arms in a 

 kind of circle to a considerable extent, 

 inclosing in this, as in a net, every insect 

 which has the misfortune to come within 

 the circumference. While the animal is 

 contracted by seizing its prey, the arms 

 are observed to swell like the muscles of 

 the human body when in action. Though 

 no appearance of eyes can be observed 

 in the polype, they certainly have some 

 knowledge of the approach of their prey, 

 and shew the greatest attention to it as 

 soon as it comes near them. It seizes a 

 worm, the moment it is touched by one of 



