THE OPHRYDIN.E. 109 



it frequently presents the appearance of a group of exquisite 

 microscopic flowers. The rim of the vase-like body is tipped 

 with a spiral of cilia, one end of the circling row descend- 

 ing a short distance down the side of the vase to a point 

 where the oral aperture of the creature is placed. When the 

 Vorticella is in search of food with its cilia in active vibration, 

 the stalk is fully extended, but at the slightest disturbance it 

 shrinks into close spiral folds so as to draw the little bell as far 

 as possible from danger. 



The Ophrydinse, another family of Infusoria, are remarkable 



for their being usually found embedded in a gelatinous mass of 



greenish colour, which is 



sometimes adherent, some- 

 times free, and may attain 



the diameter of four or five 



inches, presenting such a 



strong general resemblance 



to a mass of frog's spawn 



, -i , i nn Section of a portion of the periphery of Ophry 



as to have been mistaken dram versatile, 



frr <ann"h "From fl POTTl- showing the manner in which the individual animal- 

 cules are implanted in the mass. 



parison of the dimensions 



of the individual Ophrydia, each of which is about -JQ of an 

 inch in length, with those of the composite masses, some 

 estimate may be formed of the number included in the latter, 

 for a cubic inch would contain nearly eight millions of them ; 

 and many times that number must exist in the larger masses, 

 even making allowance for the gelatinous cushion which enve- 

 lopes the individual animalcule. 



In the water all these congregated animalcules are disposed 

 in close rows, something in the same manner as in Volvox. On 

 shaking the mass, many others show themselves within, between 

 the former, so as to form from three to five different ranks. 

 At first all the gelatinous cells appear to be connected with the 

 centre of the mass by filamentary prolongations, but these dis- 

 appear as they proceed internally, so that the middle of these 

 wonderful animated little globes seems to be hollow and full of 

 water. 



The Infusoria are almost exclusively aquatic ; most of them 

 live in ponds, morasses, pools, wells, or cisterns ; many are 

 marine, but a few are found both in sweet and saltwater. Some 



