20 THE BEGINNINGS OF LIFE. 



obvious to the two extensive and beautiful marine groups of the 

 radiolaria and foraminifera. The radiolaria are so called from 

 the raylike arrangement of their processes or pseudopodia. Like 

 the last form, they are sun-animalcules, enclosed in silicious tests 

 or shells. These shells are of remarkable beauty and variety, as 

 you will see from the photomicrograph of some of them, taken 

 with dark ground illumination. In the next two illustrations the 

 radiolaria are represented in their living state, with the rays 

 protruding from the numerous orifices. No less striking from 

 the variety and graceful sculpture of their forms are the 

 foraminifera. In their case, however, the tests or shells are not 

 composed of flint, but of carbonate of lime. The animal itself 

 is simply a point of protoplasm resembling the ama-ba, and, like 

 it, putting out processes or pseudopodia. These are often so 

 numerous that they interlace and form a protoplasmic network, 

 as you will observe from the diagram of a very graceful form, the 

 rotalia, in which the shell is many-chambered, and is covered 

 with minute pores, through which the processes are put forth. 

 Another elegant form is the miliolina, in which the shell is a 

 spiral, whose convolutions are folded over each other. In 

 another form, called by the fantastic Greek name Haliphysema, 

 or bubble of the sea, there is an approximation to the sponges» 

 for the protoplasm is enclosed in a cell built up of a mass of 

 spicules or needle-like rods, which are characteristic of the 

 skeleton of sponges, but also occur upon the integument of the 

 echinodermata, sea eggs, sea slugs, &c. In one of the latter, the 

 synapta, these calcareous spicules assume the form of beautifully 

 symetrical anchors and plates. They are shown in the photo- 

 micrograph arranged in a group. So vast has been the number 

 of the foraminifera in the geological past that whole strata are 

 composed of their fossil tests. The chalk beds are almost entirely 

 made up of them, and one species, the nummulites, occurred in 

 such vast quantities that they form a band of limestone stretching 

 from the Atlantic shores of Europe and Africa through "Western 

 Asia to Northern India and China. The photomicrograph 

 represents a section of chalk rock, with partly decomposed tests, 

 and the diagram illustrates the various forms of foraminifera 

 from the chalk. The next diagram shows several forms of 

 foraminifera, but I wish particularly to direct your attention to 

 the section of nummulitic limestone with the organisms in situ. 

 This limestone is of great interest to us as being the material of 



