7i6 SCIENCE PROGRESS 



volume is composed ; as a summary of our knowledge of the reproductive and 

 related processes in the Mammalia the book fully justifies Prof. Schafer's 

 description. 



The first chapter gives a short account of the phenomena of breeding seasons 

 in the various groups of the animal kingdom ; and it is concluded that generative 

 activity in its widest sense (including migration, etc.) occurs as a result of definite 

 stimuli, which are partly internal and partly external. It is also suggested that 

 the failure to breed in captivity, which is so often noticed, is possibly due not 

 to adverse influences acting on the generative organs but to the absence of the 

 needful external stimuli. 



The cestrous cycle in the Mammalia is next discussed ; the meaning of 

 " CEstrus," " Prooestrum," " Metoestrum " and so forth is carefully defined and 

 the various types of cestrous cycle in the different orders of mammals are 

 described. It is shown how the cycle may be affected by environment, so that 

 domestic animals often differ in this respect from their wild progenitors. The 

 relation of the cestrous cycle in the lower mammals to the menstrual cycle of 

 the human species is discussed ; and in the succeeding chapter, after fully 

 describing the changes undergone by the uterus in the various phases of the 

 cycle in man and various mammals, it is concluded that menstruation is homo- 

 logous in all essential respects with the prooestrum of the lower mammals. 



The full discussion of the purpose of the prooestral and menstrual changes 

 is again postponed until the phenomena of oogenesis, ovulation, formation of 

 corpus luteum, etc., have been described ; it is then concluded that the most 

 probable hypothesis is that the object of these changes is a preparation of the 

 uterus for the reception of the fertilised ovum — though exactly why such extensive 

 preparation should be necessary is not quite clear. Mammalian spermatogenesis, 

 the structure and movements of spermatozoa and natural and artificial insemi- 

 nation are considered, after which a chapter is devoted to the phenomena of 

 fertilisation, including a short account of various theories on the subject and 

 of telegony and artificial parthenogenesis. The Mendelian Theory is outlined 

 and some account given of the possible role in heredity of the nucleus and 

 chromosomes ; Verworn's objection to the Mendelian conception of unit characters 

 is quoted with approval, on the ground that it is inconsistent with the intimate 

 organic correlation so familiar to the physiologist and " is too morphologically 

 conceived." To the present writer it appears that this objection is valid not 

 against the Mendelian conception in its proper sense but against the assumption, 

 too often carelessly expressed, that a particular " factor " is borne by a particular 

 morphological unit ; if such a unit exists (in a chromosome or elsewhere) it must 

 exist in relation to the rest of the cell or organism and any change in that relation 

 results in the change from one Mendelian " character " to another. Interesting 

 suggestions for experiment on selective fertilisation are also given under 

 this head. 



A detailed description follows of the accessory male reproductive organs and 

 glands and of the nervous mechanism of insemination, succeeded by a chapter 

 on the Biochemistry of the Reproductive Organs contributed by Dr. Cramer. One 

 of the most valuable chapters in the book deals with the ovary and testes as 

 organs of internal secretion, showing how they are correlated with secondary 

 sexual characters and with the ductless glands and proving that the secretion 

 of the follicular or interstitial cells of the ovary provides the stimulus for the 

 prooestral or menstrual changes in the uterus. The origin and structure of the 

 corpus luteum has been described in a previous chapter; its function in main- 



