CHAPTEE XIII. 



- REPRODUCTION AND DEVELOPMENT. 



THE eternal changefulness of things is impressively typified in the 

 rapid succession of generations consequent on man's inherent mortality. 

 It is this which makes reproduction one of the three or four universally 

 essential functions of all organisms, for individuals die and must be 

 replaced if the races are to persist. The means by which this replace- 

 ment is brought about constitute one of the most elaborate of all psycho- 

 physical mechanisms, while the record of the process of the individual's 

 growth to maturity and his subsequent decadence are the history of life 

 and death, are physiology itself. To these two important subjects, 

 reproduction and development, so interwrought with life's happiness and 

 misery, so vastly complex in all their details, we can here pay but inade- 

 quate attention and give but insufficient space. We can discuss briefly 

 the bare outlines of only the somatic process, in part the physiology of 

 the organs concerned, but must leave undescribed entirely all that great 

 mass of psychological, social, anthropological, and criminological facts 

 which from any adequately broad view-point constitute part of the deep 

 problems of sex and of racial progress basal truths in human physiology 

 considered as the science of man's normal living. Even medical men, 

 the proper teachers of mankind, because of the hereditary prudery of 

 the race still reserve from common knowledge reproductive facts and 

 theory which would be of immense value to mankind, making happy the 

 lives of multitudes of boys and girls which without this needful informa- 

 tion will be stained with unnecessary disease and misery. 



It is inevitable that with so large a number of dissimilar animal forms 

 as there are (a million or so), there should be many processes of genera- 

 tion. All the forms of reproduction may be classed, however, either as 

 asexual or sexual except in the one-celled animals, the protozoa, in 

 which we find budding, simple division, spore-formation, and one or two 

 other more or less similar processes. The asexual process in multicells 

 is seen chiefly as budding in some form or other. The sexual process 

 proper involves the union of special reproductive cells which have small 

 part in the general functions of the body, and largely serve this function 

 of reproduction. The special germ-cells coming from one (the male) 

 sex are termed spermatozoa, those from the other (female) sex ova, and 

 usually their combination in fertilization is necessary for the origination 

 of a new individual. In a few cases, however, the female cells (ova) 

 develop into infertile animals parthenogenically, that is without being 

 fertilized by male protoplasm. In sexual reproduction the ovum stands 



