76 



THE AMERICAN MONTHLY 



[April, 



Professor Rogers obtained two 

 copies of tlie meter of the Archives, 

 ■one a line-meter on a copper bar, 

 "with platinum ends of the new 

 form, made and signed by Mr. 

 Tresca, now Director of the Con- 

 servatory of Arts and Meters, at 

 two o'clock on the morning of 

 February 6th, 1880; the other 

 ■an end-measure, made by M. Fro- 

 ment, which was, in 1868, found to 

 be 8.43/' longer than the meter of 

 the Archives, at ° C. 



—The twelfth volume of the U. S. 

 •Geological Survey of the Territories 

 in charge of F. Y. Hayden, has just 

 been issued. This volume is a large 

 ■quarto, and it contains Professor 

 Joseph Leidy's report on the Fresh- 

 water Rhizopods of North America, 

 illustrated by forty-eight full-page, 

 lithographic plates, with over 300 

 pages of letter-press. 



The value of this contribution to 

 the knowledge of Rhizopods cannot 

 be over estimated. Professor Leidy 

 has devoted several years to the 

 study of these minute and interest- 

 ing animals, and we need hardly 

 say that no other man, in this 

 country at least, is capable of 

 making a report like this— so accurate 

 and so good. 



We have already examined some 

 parts of the work with care ; not 

 only is it well done, from a scientific 

 point of view, but the descriptions 

 are so remarkably clear, and the 

 habits of the various species are 

 given in such an interesting way, 

 that one seems to be familiar with 

 the animal without having seen it. 

 Indeed this is a book that might 

 well be read by those who fail to 

 appreciate the attractions of micros- 

 copical study, for it is written by 

 one who is an enthusiast, we think, 

 as well as a careful observer. 



Professor Leidy has given more 



attention to the classification and 

 naming of the forms he has met 

 with, than to the elucidation of 

 structural details, but the latter have 

 not been entirely neglected. 



The class Rhizopoda, is divided 

 into five orders, viz. I. Protoplasta ; 

 II. Heliozoa; III. Radiolaria; lY. 

 Foraminifera ; Y. Monera. 



The first two orders are commonly 

 designated as the " fresh-water 

 Rhizopods," the Radiolaria and 

 Foraminifera are marine. As 

 regards the fresh-water forms. Pro- 

 fessor Leidy says : — they " are to be 

 found almost everywhere in posi- 

 tions kept continuously damp or wet, 

 and not too much shaded. They 

 are especially frequent and abun- 

 dant in comparatively quiet waters ; 

 clear, and neither too cold nor too 

 much heated by the sun, such as 

 lakes, ponds, ditches and pools. 

 They are also frequent in wet bogs 

 and savannas, among mosses, in 

 springy places, on dripping rocks, 

 the vicinity of water-falls, springs, 

 and fountains, and in marshes, 

 wherever the ground is sufficiently 

 damp or moist to promote the 

 growth of algge." 



The Protoplasta are divided into 

 two sub-orders, Lobosa and Filosa, 

 distinguished mainly by the pseu- 

 dopodia, which, in the former are 

 finger-like or lobose, and in the 

 latter filamentous. 



The Heliozoa, or "sun-aminal- 

 cules" are commonly spherical in 

 shape, with delicate pseudopodia 

 radiating from every part of the 

 surface of the body. 



After describing the various 

 genera and species, there are given 

 " Lists of Fresh-water Rhizopods, 

 indicating the many forms which 

 occur together in certain localities," 

 and a valuable bibliography of the 

 fresh-water Rhizopods. 



We regret that we cannot give a 

 more extended notice of this book, 



