128 



THE MICROSCOPE 



Fig. 117. — Foraminifera. 



The Foraminifera are from a structural point of view similar 

 to the Heliozoa, being morsels of jeUy having the power of forming 



round themselves shells of chalk 

 extracted from their food and the 

 water in which they live. These 

 shells take myriads of different 

 forms, but have one thing in com- 

 mon : they are perforated with 

 multitudinous holes through which 

 slender threads of jelly exude. To 

 this family belong the shells which 

 form chalk. Innumerable numbers 

 of these tiny creatures fall, as they 

 die, to the bottom of the ocean, 

 forming there, in the course of ages, 

 a layer of chalk which may later 

 be raised by volcanic action above the sea-level. 



Such examples illustrate the gradual development of a shell, 

 the creature in every other respect retaining its original simplicity. 

 We can now trace ■ development in a difierent direction 

 leading to more complex creatures endowed with 

 locomotion. The jeUy or protoplasm of which the 

 living animal is formed appears to slightly harden 

 all round its borders, and a creature of a more or 

 less definite shape is produced, still very elastic 

 and capable of retracting or extending itself to per- 

 haps three times its normal length. 



It has a somewhat pointed end, and the margin fig.118. 



of its body is stiU sufficiently soft to enable it to Trypano- 

 feed by absorbing into its substance through any some, 

 portion of the surface small particles of food, but 

 it cannot get outside such large things as the Amoeba. This 

 is the creature which, if it finds its way into the blood of 

 animals or men, causes in one case the tzetze-fiy disease and in 

 the other the dread sleeping-sickness, and it is known as the 

 Trypan osome. 



A further stage shows the de- 

 velopment of a flagellum, or whip, 

 which is formed by the drying up 

 and hardening of the pointed end of 

 the body. The flagellum vibrates, and 

 by its aid the creature can swim 

 about with considerable rapidity. In- 

 numerable forms of these Flagellata 

 are found in all decaying matter, and 

 their activity is surprising. Some of 

 them have further extended their cell wall into a sucker, by 

 which they attach themselves to some fixed object, and whole 



Fia. 119.— Flagellata. 



