Jan. 8, 1880] 



NATURE 



235 



to the naked eye. But what most struck me at first in 

 this animal was' that it seemed literally to have no other 

 nourishment than the coarse sand by which it was 

 surrounded. And then when, armed with scalpel and 

 microscope, I ascertained something of its organisation, 

 what unheard-of marvels were revealed ! In this body, 

 the walls of which scarcely reach the sixteenth part of an 

 inch in thickness, I could distinguish seven distinct layers 

 of tissue, with a skin, muscles, and membranes. Upon 

 the petaloid tentacles I could trace terminal suckers, 



which enabled the Synapta to crawl up the side of a 

 highly-polished vase. In short this creature, denuded to 

 all appearance of every means of attack or defence, 

 showed itself to be protected by a species of mosaic, 

 formed of small, calcareous, shield-like defences, bristling 

 with double hooks, the points of which, dentated like the 

 arrows of the Carribeans, had taken hold of my hands. 

 If one of these Synapta is preserved alive in sea-water for 

 a short time, and subjected to a forced fast, a very strange 

 phenomenon will be observed. The animal, being unable 



Fig. 3.— Synapta duv 



to feed itself, successively detaches various parts of its 

 own body, which it amputates spontaneously." 



Although most of the illustrations in this volume are 

 very good, and some arc good works of art, there are 

 also several which are very poor, and quite unworthy of 

 the text. This is especially the case among the smaller 

 birds, several of which are unrecognisable. A few also 

 have been wrongly named, representing very different 

 creatures from those they are said to be. The most 

 prominent defects of this kind are the figure of the Leu- 

 coryx antelope, which is named Saiga tariarica, and 



ON THE SECULAR CHA.XGES IN THE ELE- 

 MENTS OF THE ORBIT OF A SA TELLITE 

 REVOLVING ABOUT A PLANET DISTORTED 

 BY TIDES l 



'THE investigation which forms the subject of this 

 -*■ paper is entirely mathematical, and is therefore not 

 of a kind to be easily condensed into a short account. 



This paper is the fifth of a series (of which notices 

 have from time to time appeared in Nature) in which 



1 An account of a paper by G. H. Danvii 

 Society, on Dec-;. 



F.R.S., read before the Royal 



that of two humming-birds, which do duty for sun-birds. 

 These oversights, which no doubt occurred in the London 

 office, since they are far too gross to be imputed to the 

 author of the book, should be corrected in another 

 edition ; and if the publishers will substitute better figures 

 for those of the stone- chat, hedge-sparrow, dipper, Java- 

 sparrows and some others which are barely recognisable, 

 the work will be one of permanent use and interest, both 

 as an illustrated manual of the families of the vcrtebrata 

 and a popular introduction to general natural history. 



A. R. \V. 



I have endeavoured to trace the various effects on the con- 

 figuration of a planet and satellite, which must result from 

 tidal friction— the tides in the planet being cither a bodily 

 distortion or oceanic. The investigations are, I think, not 

 without interest as a branch of pure dynamics, but this 

 side of the subject is too complicated to be made intelli- 

 gible without mathematical notation, and it would occupy 

 too much space to explain the methods of treatment. 



There is, however, another side of the subject, which 

 must, I think, attract notice, or at least criticism, and 

 this is the applicability of the results of analysis to the 

 history of the earth and of the other planets. 



