MORGAN’S “HEREDITY AND SEX”: 
A REVIEW 
By E. G. Conklin 
HIS book is the outgrowth of the 
Jesup Lectures for 1913 which were 
given by Professor Morgan at the 
American Museum of Natural His- 
tory. It is a very difficult thing to make a 
book interesting to the general public and 
at the same time valuable to scientific 
readers, but this difficult task Dr. Morgan 
has accomplished in an admirable manner. 
His book is a work of extraordinary interest 
to the intelligent layman and at the same 
time one of great value to professional biol- 
ogists, and its wide success is attested by 
the fact that the first edition was exhausted 
and a new one issued within a year. 
The book embodies the results of a large 
amount of research work by Dr. Morgan and 
his pupils as well as by many other investi- 
gators. The subjects dealt with in the eight 
chapters are: Evolution and Sex; The 
Mechanism of Sex Determination; The 
Mendelian Principles of Heredity and their 
Bearing on Sex; Secondary Sexual Characters 
and their Relation to Darwin’s Theory of 
Sexual Selection; The Effects of Castration 
and Transplantation on the Secondary 
Sexual Characters; | Gynandromorphism, 
Hermaphroditism, Parthenogenesis and Sex; 
Fertility, and Special Cases of Sex Inherit- 
ance. Hach of these general topics is dealt 
with in a manner which is not only instructive 
but also illuminating and interesting. As to 
the “Evolution of Sex’”’ it is shown that we 
know actually nothing about the manner in 
which sex has come to be. Sexual reproduc- 
tion brings about many new combinations of 
characters but such recombinations do not 
furnish the materials for evolution as Weis- 
mann assumed. However these new com- 
binations of ancestral characters produce a 
ereat amount of individual variation and this 
may be beneficial to a species in helping it to 
survive. Furthermore if a new character 
arises in a single individual it may be grafted 
on, as it were, to the species by sexual re- 
production. 
1 HprReDITY AND Sex, by Thomas Hunt Mor- 
gan, Ph.D. Professor of Experimental Zo6logy in 
Columbia University, pp. ix + 292 with i121 illus- 
trations in the text. Columbia University Press: 
New York, 1913. Revised Edition, 1914. 
194 
There is an interesting discussion of the 
various types of accessory organs of repro- 
duction which serve to bring the spermatozoa 
and ova together and of the secondary sexual 
characters which distinguish males and 
females such as brilliant colors, instincts and 
behavior in courtship. “In man courtship 
may be an involved affair.... Nowhere in 
the animal kingdom do we find such a mighty 
display; and clothes as ornaments excel the 
most elaborate developments of secondary 
sexual characters of creatures lower in the 
scale.’ 
With remarkable clearness and brevity the 
author presents the facts of the complicated 
structure of the germ-cells, their origin, 
maturation, union in fertilization, the way 
in which sex is determined and the mechanism 
of hereditary transmission. He accepts un- 
reservedly the view that sex is determined 
at the time of fertilization; if the egg is 
fertilized by one type of spermatozo6n a male 
is produced, if by the other type a female 
results. He also holds that the evidence is 
“almost convincing in favor of the view that 
the chromosomes are the essential bearers 
of the hereditary qualities.” In favor of 
the chromosomal theory of heredity he pre- 
sents evidences drawn from cytology, from 
experiment and from sex-linked inheritance. 
The latter is a type of inheritance, first clearly 
distinguished by Morgan, in which characters 
are transmitted to male or female offspring 
in exactly the way in which certain chromo- 
somes are transmitted. On the other hand 
in sex-limited inheritance “the secondary 
sexual characters appear in one sex only and 
are not transferable to the other sex without 
an operation.” 
After discussing the principles of inherit- 
ance discovered by Mendel the author 
presents the results of his own work on the 
inheritance of sex-linked characters in the 
fruit fly. This is perhaps the most important 
part of this book, as it is one of the most 
valuable contributions to the study of hered- 
ity which has been made in recent years. 
The author concludes “‘that when inheritance 
factors lie in different chromosomes they 
freely assort and give the Mendelian expecta- 
tion; but when they lie in the same chromo- 
