PROTOZOA 59 



A single ounce of sand from the Antilles was calculated 

 to contain over three millions. The bottom of the ocean, 

 up to about 50 on each side of the Equator, and at 

 depths not greater than 2400 fathoms, is covered with 

 the skeletons of these animals, which are constantly 

 falling upon it (Globigerina ooze). Their remains consti- 

 tute a great proportion of the so-called sand banks 

 which block up many harbors. Yet they are descend- 

 ants of an ancestry still more prolific, for the Foraminif era 

 are among the most important rock-building animals. 

 The chalk cliffs of England, the building stone of Paris, 

 and the blocks in the Pyramids of Egypt are largely 

 composed of extinct Foraminifers. Foraminifera are 

 both marine and fresh-water, chiefly marine. 



The sun animalcule (Actinophrys sol\ one of the Heli- 

 ozoa, is common in the slime on the sides of aquaria. 

 Its spherical body, composed of frothy protoplasm, 

 bears numerous stiff radiating processes by means of 

 which the animal moves about and captures its food. 



A Radiolarian differs from a Foraminifer in secreting 

 a siliceous, instead of a calcareous, shell, studded with 

 radiating spines ; and in the central part of the body is 

 a perforated membranous sac containing a nucleus or, 

 sometimes, several nuclei. The most of the protoplasm 

 of the body lies outside the sac. Radiolarians are more 

 minute than Foraminifera, but as widely diffused. They 

 enter largely into the formation of some strata of the 

 earth's crust, and abound especially in the rocks of Bar- 

 badoes and at Richmond, Va. The living forms are 

 marine. 



CLASS 2. Mycetozoa 



These organisms are frequently classified among the 

 plants under the name of "slime molds." They consist 

 of masses of protoplasm of various sizes and colors, and 



