4 THE AMERICAN MONTHLY [January, 



part they play in nature, owing to their immense numbers. The sediment 

 of the Atlantic ocean is largely composed of their shells, which form 97 per 

 cent, of the ooze.* Paris is almost built up of them ; likewise, the Pyramids 

 of Egypt. The European chalk and the green sands of our own countr}- are 

 chiefly formed of their remains. In the island of Barbadoes rock strata of 

 the tertiary period, 1,100 feet in thickness, are full of the same. ' They form 

 the chief component of a hmestone band, often 1,800 miles in breadth, and 

 frequently of enormous thickness, that may be traced from the Atlantic shores 

 of Europe and Africa through Western Asia to Northern India and China, 

 and likewise over vast areas of North America. 'f But perhaps no better 

 idea of their enormous numbers can be given than by stating the results of 

 several counts or estimates by different observers. D'Orbigny counted 6,000 

 individuals in an ounce of sand from the Adriatic, and estimated that there 

 were 160,000 in a gramme of selected sand from the Antilles. Schultze found 

 I, =500,000 in i^ grammes of sand from the coast of »Sicily. Leidy obtained 

 over 38,000 to the ounce at Atlantic City, j 



Furthermore, thev cannot fail to attract because of the beautiful and varied 

 shapes which they display. Some of the most exquisite of all microscopic 

 objects belong to this class. And not only the shells themselves, but their 

 delicate markings command attention, being fully as fascinating as those on 

 the diatoms which have so monopolized the time and patience of all lovers 

 of the tube. But over and above all these points there is an absorbing inter- 

 est attaching to the Rhizopods because of their place in the natural scale. 

 They are the lowest of all animal forms. In studying them we are studying 

 life at its verv foundation. If there is any truth in evolution, we are here at 

 the first round of the ladder. Thus, geographically, chronologically, geo- 

 logically, aesthetically, and biologically, my subject has claims upon you all. 

 What, then, are the Rhizopods.? They are ' a class of the animal sub-kingdom 

 Protozoa, '§ ranking below the worms and the rotifers, below the polyps and 

 the jelly-fish, below even the infusoria — ' animals, because the}' depend on 

 preformed protoplasm, and do not possess a cellulose cell-wall ; protozoans, 

 because not differentiated into cells. '|| Mark that latter point, for thus it will 

 be seen that they are not only the last of several subdivisions ; they are on 

 one side and all other animals whatsoever on the other. The Protozoa and 

 the Metazoa are to-day the two most noticeable divisions of the animal king- 

 dom, the former being ' either single cells, or aggregates of similar cells cor- 

 responding to the mulberry stage of higher types, the latter being individual- 

 ized organisms, every part of which contributes to the life of the whole, '^ 

 the mulberry mass developing into parts mutuall}' dependent. 



Such are Rhizopods, systematically speaking ; but when you ask me to 

 describe them anatomically I am at a loss. In most animals it is the com- 

 plexity of structure that puzzles one, but in these it is the very opposite. 

 The simplicity is so great that there is positively almost nothing to mention. 

 When I have told you that they are bits of jelly, that they have an outside and 

 an inside, a spherule of protoplasm more distinct than the rest, and a vesicle 

 which appears and disappears, I have said all there is to be said. You may 

 call the outside the ectosarc and the inside the endosarc, but that is only to 

 substitute Greek for English terms. Except that the inside is more granular 

 than the outside, there is no difference. ' The exoplasm and endoplasm,' 

 says Lankester, 'described in amoebae, &c., by some authors, are not dis- 

 tinct layers, but one and the same continuous substance — what was inter- 

 nal at one moment becoming external at another, no really structural difter- 



* Carpenter, The Microscope, ■g. ^(sq. t /^^»i, p. 580. t Leidy, Rhizopods. 



%Mic. Diet. II M'Alpine, Biol. Atlas. 'i. Cs.r-^e.nt&'c , The Microscope . 



