NATURE STUDY IN SCHOOLS. 137 



opening the cilia are a little longer than elsewhere. This is the mouth and 

 is permanent. The food is taken into it by the aid of the long cilia and 

 passes down into a gullet, (see Fig. 68) but afterwards form balls which are 

 scattered through the surrounding protoplasm and in which the food is di- 

 gsstad ( see Fig. 68, D. ) as we found in amoeba. When the nutritious 

 matter has all been assimulated. the indigestable portion of the food balls is 

 thrown out at the point mentioned as the heel of the slipper, breaking through 

 the ectoplasm with each successive discharge. This heel is known as the 

 anal spot. 



Reproduction. Multiplication of the species is accomplished as in 

 amoeba, by division, and each individual may divide several times, as in 

 amoeba, without fertilization, but ultimately two slipper infusoria are seen to 

 come together and remain in contact for some time. During this time, some 

 of the fluid contents of the nuclei are exchanged. Immediately after sepa- 

 rating, division takes place in both individuals. 



Irritability or Nervous System. The fact that slipper infusoria move 

 rapidly shows that the nervous system is better developed than in the 

 amoeba. 



Encystment. As in amoeba, under similar circumstances, the slipper 

 infusoria may become encysted. 



Advancement. In reproduction we find something akin to fertilization 

 in what is known as conjugation. A summary of all these points of advance- 

 ment will show us that both physically and mentally the slipper infusoria 

 are considerably higher than the amoeba. 



VORTICELLA, OR BELL INFUSORIA. 



In this peculiar form of Protozoa we find the next stage of advancement. 

 The species is found on the stems of fresh water plants in the form of mi- 

 nute branching colonies. 



Form. Each individual of this colony is bell-shaped with a ciliated disk. 

 See fig. 68, B. 



Structure. While the outer and inner layers of protoplasm are a little 

 b2tter developed even than in paramoecium, there is a general resemblance. 

 The same ectoplasmic and entoplasmic structure extends into the stems, by 

 which the bells are attached to a common stalk, or directly to the plant by 

 one stem. 



Digestion. The vestibule Avhich leads into the mouth in the bell ani- 

 malcules, is found at one side of the ciliated disk, (see Fig. 68, V o ) and the 

 motion of the cilia causes the water, with its accompanying food, to flow 



