October 13, 1892] 



NA TURE 



559 



reply to Prof. Vines' citation of the parthenogenetic fungi, 

 that not only sexual forms may vary into new species. 



It is to the last essay, that on " Amphimixis, or the 

 essential Meaning of Conjugation and Se.xual Reproduc- 

 tion," that most attention will be directed Here there 

 is a full statement, with important additions and altera- 

 tions of the central part of Dr. VVeismann's theories. 

 However they may bulk in public imagining, questions 

 of acquired characters, of retrogressive metamorphosis, 

 and so forth, are side issues of a search for the morpho- 

 logical expression of the processes of variation. 



Originally Weismann explained the two successive 

 divisions of the nucleus of an unfertilized egg which form 

 the two polar bodies as, in the case of the first, an 

 extrusion of that nuclear plasm which, having served to 

 guide the maturation of the egg, became useless when 

 the egg was mature ; and in the case of the second, as a, 

 halving of the nuclear substance to make way for the 

 incoming sperm-plasm. 



In parthenogenetic ova, one division and only one was i 

 predicted and found. It was suggested that parallel 

 processes occur in spermatogenesis. 



Subsequent research by O. Hertwig and others has 

 brought to light these parallel processes, and Weismann^ 

 seeking for a sign, got rather more than he anticipated. 

 For the processes in spermatogenesis show first a 

 doubling of the germ-plasma, and then two successive re- 

 ducing divisions, and it has been shown that exactly this 

 happens in ova also. Accordingly, Weismann rejects 

 his original explanation of the first polar body as an 

 extrusion of ovo-genetic nucleoplasm, and the new 

 problem comes to be, what is the cause of that doubling 

 of the nucleoplasm which in primitive sperm and germ 

 cells precedes the two reducing divisions .'' 



Weismann supposes that the ancestral plasms or units 

 of heredity, to which he gives the name " ids," are 

 arranged in "idants," or nuclear rods. The doubling 

 process takes place normally by longitudinal division 

 and simply doubles the number of idants without altering 

 the arrangement of " ids." By this method the num. 

 ber of possible combinations is increased without 

 alteration of the ids. The process is a mechanical one 

 to increase the chances of combinations when the idants 

 of sperm and germ cells meet. If the idants were 

 coloured rods, to be arranged in pairs — say black, white, 

 red, and yellow for four sperm idants, and orange, green, 

 blue, and crimson for those of the egg-cell — obviously 

 only four pairs are possible. The black would have to 

 unite with one of the four others. But if before the 

 arrangement in pairs each rod were split in two, there 

 could be two combinations for black , and so on for the 

 others. No doubt in many cases the number of idants 

 is far greater than four, and the mechanical arrangement 

 for variations correspondingly greater. From the large 

 number of possible combinations there come the relative 

 few individuals of the next generation, and there is thus 

 a basis for the lawless and apparently capricious appear- 

 ance of varieties. Next in importance comes Dr. 

 Weismann's belief, based on theoretical considerations, 

 and supported by experiments on Cypris, conducted for 

 seven years, that in parthenogenetic reproduction 

 heritable variations may occur. But they are far less 

 frequent than in sexual reproduction. But the whole of 

 NO. 1 1 98. VOL. 46] 



this essay is full of intricate and curious speculation, 

 speculation which will have to come before every 

 student of biology, and which, whether much or little of 

 it becomes incorporated in the body of accepted know- 

 ledge, will at least play a large part in guiding and 

 stimulating present research. P, C. M. 



ELEMENTARY CHEMISTRY. 



The Standard Course of Elementary Chemistry. By E. 



J. Cox, F.C.S. Pp.344. (London: Edward Arnold.) 



THIS book consists of five parts, which may be 

 obtained separately or bound up in one volume. It 

 is based upon the syllabus prescribed by the Education 

 Department for teaching chemistry as a class or specific 

 subject, and professes to lead the beginner from the 

 " familiar " to the " less known " by means of " investiga- 

 tion," the teaching thus afforded being regarded as a 

 branch of mental education as well as of useful know- 

 ledge. The five parts deal respectively with the pro- 

 perties of the common gases, the atmosphere, water, 

 carbon and non-metallic elements, and with metallic 

 bodies, combination, symbols and formulas. 



The general plan of the book and the manner in which 

 the subject is approached, have a good deal to recom- 

 mend them ; the detailed treatment contains, however, 

 much which could be improved, and unfortunately much 

 which the learner will have to forget as he progresses in 

 the study of his science. In the opening chapter, 

 evidently for the sake of simplicity, the author uses the 

 term heat in place of temperature. More confusion on 

 the subject of heat is made later on by the use of equa- 

 tions, such as 



Chalk ) i Lime 



and > yield,, and 



J/eat ) ( Carbonic Acid Gas." 



which appears to attribute to heat a material existence ; 

 and even more unsatisfactory are bald statements to the 

 effect that " no heat is produced in the formation of a 

 mixture. Heat is produced in the formation of a chemical 

 compound." 



Considerable space is occupied in the comparison of 

 the affinities of the elements. Because certain metallic 

 oxides, including iron-oxide, are reduced when heated in 

 a stream of hydrogen, the affinities of the metals for 

 oxygen are said to be weaker than that of hydrogen for 

 oxygen. In the case of iron and steam the author has to 

 note that the inverse change — the oxidation of the metal 

 by steam — readily occurs, and that the former statement 

 as to the affinities of iron and hydrogen for oxygen, is 

 apparently contradicted. This contradiction might have 

 indicated the futility of attempting to compare affinities 

 in a general way and not with reference to the special 

 conditions under which the experiments were performed. 

 The inverse change in the case of iron is said to occur 

 when the " temperature " is favourable, but in reality the 

 active masses of the reacting materials determine the 

 direction of the change. 



Inaccurate statements are numerous. Hydrogen is 

 said to form " one-third part of water by volume," " a 

 formula " is stated to " represent a molecule," and a base 

 is given as " a compound of a metal with hydrogen and 



