No. 1, November, 1921] GENETICS 15 



92. Haecker, Valentin. Allgemeine Vererbunsglehre. [General genetics.] W X 2^ cm., 

 ix + 444 V-t H9 fig. Friedr. Vieweg & Sohn: Braunschweig, 1921. — The book consists 

 of 37 chapters arranged in 7 sections. The contents of these 7 sections, together with the 

 author's views of chief theoretical interest, are briefly as follows: Section I. Early known 

 facts of heredity in man and domestic animals and the development of ideas of heredity are 

 reviewed. The author gives (1) the early classification of facts of heredity by means of so- 

 called "laws"; (2) statistical laws, as those of ancestral contributions, regression (Galton); 

 (3) development of statistical methods; and (4) origin and methods of genealogy. — Section II 

 is devoted to (1) morphological basis of heredity; (2) structure, chemistry, and physiology 

 of protoplasm; (3) cell theory and structure of nucleus. The division of organisms into cells 

 is held to be significant in the development of form and in physiological processes. Several 

 theories of the mechanics of cell division are discussed without special support of any one. 

 Somatic and germ cells are recognized early in embrj'onic development. Maturation and 

 structure of mature germ cells, attraction of egg and sperm, and the process of fertilization 

 are described. Complete or partial separation of egg chromosomes and sperm chromosomes 

 (gonomery) in earlj^ spindles or nuclei of the embryo is described in several cases. The history 

 of germ cells in plants is briefly related. Size differences among chromosomes may be due in 

 some cases, at least, to imequal grow^th of the chromosomes. The number of chromosomes is 

 given for many species, and the variation in number within single species and among species 

 of larger groups is described. Diminution in the size of chromosomes in evolution appears to 

 occur simultaneously with a decrease in number. Maturation divisions in animals are homolo- 

 gized with those in plants. Maturation is regarded phylogenetically as rudimentary spore 

 formation. — Section III. Older morphological theories of heredity (Darwin's pangenesis, 

 Galton's stirps, etc.) are discussed. Continuity of germ-plasm is regarded by the author 

 as forming the foundation of the theory of heredity. The mechanistic theories of Nageli, 

 Roux, Weismann, and others are described. The contrast between nucleus and cytoplasm 

 as agents in heredity has been over-emphasized for in general the action of the 2 is harmonious. 

 Though it is conceivable that somatic induction may impress changes upon germ cells follow- 

 ing somatic modification, it is scarcely possible that the chain of events would be reversed and 

 produce the same somatic modification in the offspring. The medical practice of calling dis- 

 eases hereditary when they are merely congenital, owing to germinal or intra-uterine infection, 

 is criticized. Satisfactory evidence of the inheritance of injuries, functional changes, and 

 psychic acquisitions has never been produced; but practical breeders and some others believe 

 in such inheritance. An explanation of supposed inheritance of acquired characters by paral- 

 lel induction, especially indirect parallel induction (through sense organs and the nervous 

 system), is given with implied approval. Parallel activation, calling into action certain ones 

 of a limited number of capacities in the parent and offspring, may be the explanation of 

 some cases. Parallel reduction, loss of certain characteristics through general chemical 

 change in both parent and offspring, is suggested to explain some cases. Similar 

 modifications of parent and offspring may also easily arise owing to general weakening 

 through poisons (germinal injury, blastophthoria). New hereditary factors have been 

 produced (Tower's beetles) by direct environmental action on germ cells. Besides offering 

 the usual explanation for xenia and certain bizarre phenomena, the author suggests that 

 in some cases these phenomena may be the result of hormone (?) action of the male ele- 

 ments. Graft hybrids are described. Weismann's sj'stem of idants, ids, determinants, and 

 biophores is discussed in relation to maturation, amphimixis, and embryonic development, 

 with brief comment in view of more recently discovered phenomena. Weismann's theory is 

 regarded as neo-preformationist, in contrast to those of O. HERTwaG and others which are 

 neo-epigenetic. — Section IV. The development of pre-Mendelian ideas of heredity, termi- 

 nology, classification of hybrids, and sterility are discussed. Mendel's law is separated into 

 3 parts: Law of uniformity in Fi, law of segregation, and law of independent assortment; 

 the widespread application of these laws is demonstrated by numerous examples. Presence 

 and absence hypothesis is accepted in explanations. Multiple allelomorphs, such as factors for 

 gray, black, and chocolate in mice, are defined as 2 or more factors which represent different 

 grades of the same character. Cases of polymer)'^ are discussed. Inheritance of sex, sex- 



