1892.] MICROSCOPICAL JOURNAL. 179 



did me, especially when you compare the number of genera of 

 the Radioiaria with those of the fresh-water Rhizopods (both 

 orders included) or of the Desttiids or Diatoms. 



The genera of the fresh-water Rhizopods described by Leidy 



number 30 



Of the Dcsmids^ as given by WoUe 19 



Of the Diatoms 1 35 



While the Radioiaria alone, as given by Haeckel, number 739 



It was enough to frighten one to think of attacking that huge 

 host. In fact, I w%as so totally unprepared for anything of the 

 sort by the books at my command, that I was perfectly dazed 

 when the librarian handed me three bulky quartos, no mean load 

 for a man to carry, all devoted to this one order of the Rhizo- 

 pods. It gave me a wider conception of the infinity of nature than 

 I had ever had before, for which I was thankful, but the first 

 etlect was to take all the courage out of me. It was altogether 

 too big a contract^ and it seemed utterly useless to attempt to 

 ofier any scheme of classification for the beginner. But, as I con- 

 sulted the work, my eye fell upon a statement that reassured me, 

 namely, that of the 4,300 and more species now known, no less 

 than 3,500 were added by the Challenger Expedition, the ma- 

 terial of which is not to be obtained, and therefore the species are 

 practically cut down from over 4,000 to some Soo and the genera 

 from 739 to about 163, if I remember right. Indeed, for most of 

 us, they are cut down still further, namely, to those which are to 

 be found in the Barbadoes earth., which is the only material at 

 conimand. Now Ehrenberg found in this deposit about 3S2 

 species, which he arranged in some, 42 genera. I decided, there- 

 fore, to confine myself to the genera mentioned by Ehrenberg, but 

 making use of the classification of Haeckel, which adds some- 

 what to the number, a single genus of Ehrenberg being divided 

 by Haeckel into two, three, or more genera. Now this gives us 

 in all some 56 genera, or about the same number as we considered 

 in the case of the diatoms, and reduces the task within bounds, be- 

 sides being all that it is necessary for any one to know, unless he 

 wishes to study the material from the Nicobar Islands, or is for- 

 tunate enough to obtain some of the deep sea dredgings from the 

 South Pacific or South Atlantic. In the North Atlantic these 

 forms are rare. I examined some dredgings at difterent depths 

 from that quarter before I learned that fact and had my lal)or for 

 my pains. 



These fifty-six genera, then, fall into two great groups, namely : 



A. Peripylcea. 



B. Mono'pylcea. 



In the first the central capsule is spherical and has pores dis- 

 tributed all over it. In the second it is cone-shaped., and only the 

 base of the cone is perforated. Although it is often hard to dis- 



