POND LIFE. 249 



it a cluster of very fine threads, each of which bears a very beauti- 

 ful urn. These are Vorticellce. or Bell-animalcules. If you look 

 very closely you will find that each one contains a nucleus, and 

 also you will notice a commotion in the water, so that any little 

 floating bodies are caused to run round and round as if in a whirl- 

 pool. This is caused by a ring of hairs round the mouth of the 

 urn, which are continually bending down and up again in turn, pro- 

 ducing an appearance as though the rim of the urn were revolving. 

 What really happens is this : one hair bends towards the one next 

 it, which a moment later also bends towards the hair next beyond 

 it. But by this time the first hair has straightened itself again, 

 and by the time that a third has bent towards the fourth, the 

 second is upright again, and so on around the whole ring. In 

 this way the hairs round the rim of the urn convey the impression 

 that it is rotating, and they move so fast that you cannot see the 

 individual hairs, but only receive the general impression. If, 

 however, you place a drop of chloroform in the water under the 

 microscope you may observe the motion becoming gradually 

 slower, and may see exactly how it takes place. 



There is another structure in this animal which you must 

 notice. In the centre of the bell is a kind of funnel leading 

 down into its middle ; it is in fact a funnel, and does duty as a 

 mouth. It passes straight from the outside into the middle of 

 the body, which consists of soft pulp. So that you observe in 

 this animal an advance upon the very primitive structure of the 

 Amoeba ; that is, that one portion of the body is set apart for the 

 reception of food; it is in fact an "organ." 



These Bell-animalcules, as they are called, are very sensitive to 

 disturbance, and a very gentle tap on the microscope is sufficient 

 to make a whole colony draw in, by the rapid contraction of their 

 stalks. Although so fine, the stalk is very curiously constructed. 

 Down the middle of it you may see a very thin hair-like fibre, 

 much thinner than the rest of it, which shrinks when the animal 

 withdraws itself, the consequence being that the stalk coils up into 

 a series of spirals ; this fibre, therefore, is the first instance which 

 has come before us of a muscle. 



Like the Amoeba, and many of those plants we have considered, 

 the Voriicella reproduces itself by dividing, and this it does longi- 



