46 



NATURAL HISTORY 



proper nidus to attach itself to, it spins a very delicate 

 tin-ead, like a spider's web, one end of which it fixes to 

 the substance it has selected : this filament, when drawn 

 out to the proper length, increases in size, and assumes 

 the deep blue colour of the indigo, while the end of the 

 stalk which it left shoots forth a fresh cluster. 



The current above mentioned is sometimes produced 

 without any revolution of the cluster of globules ; at other 

 times I have observed the whole cluster to revolve. 



The magnifying power which I employed, while 

 making the drawing, figure 19, was nearly 500 times : 

 under a power of 200 they resemble figure 21, and a 

 greater number of branches may be seen at once. The 

 medium diameter of the clusters, while attached to their 

 branches, I find to be about the 800th part of an inch ; 

 and when fully developed and separate about 1 -400th 

 of an inch. 



Muller discovered them in river-water, in the month 

 of November. Those on which the above observations 

 were made, I found in the month of June, in some pond- 

 water. 



37. VoLvox globator. The globe Vohox. — This po- 

 pular and diverting animalcule was discovered by Leeu- 

 wenhoeck, and has been described by all subsequent 

 writers on microscopic objects. As its name imports, it 

 is of a globular form ; its colour is usually a light 

 green, though I have met with some of an orange 

 brown, which, however, are generally smaller than the 

 green ones. The envelope is composed of a diaphanous 



