SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VE|KTEBRATA. 

 a. Embryology.f 



Sexual Dimorphism among Animals. X — J- T. Cunningham has 

 made a careful study of the problem of sexual dimorphism in the animal 

 kingdom. His book contains seven chapters discussing and interpreting 

 particular cases, arranged according to the various classes, and an intro- 

 ductory chapter expounding the general theory which the bulk of the 

 volume is intended to confirm. We shall try to indicate briefly what 

 the author's evolutionary position is. 



(1) Observed hereditary differences may be included in three 

 categories : — diversity (of species, genera, &c), polymorphism (including 

 dimorphism), and metamorphosis (marked differences between different 

 stages in the life-history). The problem is to discover the causes which 

 have produced these three kinds of structural difference in animals. 



To those structural differences which are due to " modifications," i.e. 

 the structural results of environmental and functional influences operat- 

 ing upon the body, but not proved to be transmissible, Mr. Cunningham 

 refers later on, and postulates their transmissibility. 



(2) The diagnostic characters which express what the author calls 

 diversity cannot all be regarded as of use or significance in the struggle 

 for existence, as is illustrated by the cases of dab, flounder, and plaice, 

 in regard to which it is stated that the theory which refers the specific 

 peculiarities of these three fishes to the natural selection of indefinite 

 variations is " unsupported by any evidence." Such specific characters 

 are " the necessary consequences of growth and the conditions of life." 

 [We may note (a) that fuller knowledge has shown the advantageous 

 character of many minute features which did not at first suggest the 



* The Society are not intended to be denoted by the editorial " we," and they do 

 not hold themselves responsible for the views of the authors of the papers noted, 

 nor for any claim to novelty or otherwise made by them. The object of this part of 

 the Journal is to present a summary of the papers as actually published, and to 

 describe and illustrate Instruments, Apparatus, &c, which are either new or have 

 not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so called, 

 but also those dealing witli Evolution, Development, Reproduction, and allied subjects. 



X ' Sexual Dimorphism in the Animal Kingdom. A Theory of the Evolution of 

 Secondary Sexual Characters,' London, A. & C. Clack, l'JOO, xi. and 317 pp., 32 tigs. 



