8 4 8 



THE POPULAR SCIENCE MONTHLY 



Our author does not attempt in this vol- 

 ume to give us a complete exposition of 

 mental science. He has, indeed, to deal 

 with subjective psychology and with objec- 

 tive psychology, but he treats these aspects 

 of mental study in relation to the third 

 great mental division, the organic conditions 

 which are the latest results of scientific in- 

 vestigation. From this point of view, the 

 whole subject assumes a new interest, and 

 becomes far more practical than by the pre- 

 vious partial modes of examination. Dr. 

 Bastian has done all that it was possible to 

 do to bring his topic within the range of 

 popular apprehension. Much of his volume 

 will be read with pleasure and profit by all 

 classes ; but much of it also requires study 

 and a mastery of its indispensable techni- 

 calities. The work can not be put to its 

 proper and highest use unless the objects 

 of which it treats are to a certain extent 

 made real to the mind of the student. Dia- 

 grams, of which there are a great profusion, 

 and finely executed, are helps, but they can 

 n#t be put in the place of the objects they 

 represent without a sacrifice of the first 

 condition of true scientific knowledge the 

 briuKins; of the mind into contact with the 

 real things. But there is happily no seri- 

 ous impediment to this manner of study. 

 The brains and nervous parts of animals 

 are to be had anywhere in abundance and 

 in great variety. It is by no means expect- 

 ed that the reader or student will be able 

 to verify the whole course of illustration in 

 this volume, nor is it at all necessary. But 

 it is necessary that he should become ac- 

 quainted with the rudiments of the exposi- 

 tion by direct observation, so that he will 

 have clear and precise ideas in relation to 

 its subject matter, such as will conduce to 

 a genuine understanding of the general sub- 

 ject. We commend this work especially to 

 teachers, and venture to affirm that if they 

 will form classes in it, not with a view to 

 the slavish acquisition of its contents, but 

 to master portions of it so that the rest 

 may be read intelligently, it will prove in- 

 valuable both as a means and an end of 

 education. 



Dr. Bastian's book was written as a con- 

 tribution to the "International Scientific 

 Scries " ; but, as the author found it impos- 

 sible to do justice to the subject within 



the limits prescribed for those works, his 

 volume has been separately issued in this 

 country. 



Degeneration : A Chapter in Darwinism. 

 By Professor E. Bay Lankester, F. R. S. 

 London : Macmillan k Co. 1880. Pp. 

 15. Price, 75 cents. 



Natural selection may have operated to 

 produce present organic forms in three dif- 

 ferent ways. Organisms may have been 

 elaborated in structure with a growth in 

 variety and complexity of the conditions to 

 which they were subjected ; they may have 

 remained for a long period without any 

 change, when the conditions have been im- 

 mobile ; or, the conditions having become 

 simpler, they may have lost in structure. 

 In accounting for present forms, naturalists 

 have given little heed to the last of these 

 processes, but have endeavored to explain 

 nearly all cases (except those of the para- 

 sites, which are generally recognized as de- 

 generate forms) on the basis of the first two 

 processes. In the discourse before the Brit- 

 ish Association, which forms this volume, 

 Professor Lankester takes issue with this 

 view, and argues in support of the thesis 

 that degeneration is an important process 

 in organic evolution. He contends that 

 many problems are helped to a solution by 

 this hypothesis, which without it are hope- 

 lessly obscure, and that the evidence in its 

 favor is of a high order. His argument is 

 based upon the evidence furnished by the 

 changes through which the egg passes in 

 its development into the young creature. 

 As is well known, the forms through which 

 it passes are those that belonged to its an- 

 cestors, and these are reached in the order, 

 there is good reason to believe, in which 

 they were acquired by these ancestors. 

 This " recapitulative development " is often 

 very imperfect, many characteristics are ob- 

 scured or obliterated, but none appear that 

 did not at some time belong to the creature's 

 progenitors. Where these changes are dis- 

 tinct, then, the pedigree of an organism can 

 be traced by them with certainty. A num- 

 ber of cases of degeneration are cited by 

 Professor Lankester, the two most impor- 

 tant being the ship's barnacle and the as- 

 cidian phallusia. In the case of the bar- 

 nacle, the egg gives rise to an actively swim- 



