74 REPRODUCTION AND LIFE HISTORY. 



they are. Many of the most authoritative biologists are at 

 present of this opinion. On the other hand, many still 

 maintain that profound changes due to function or environ- 

 ment may saturate through the organism, and affect the 

 reproductive cells in such a way that the changes or 

 modifications in question are in some measure transmitted 

 to the next generation. The question remains under dis- 

 cussion, but the probabilities are strongly against the 

 transmissibility of acquired characters. 



It is' important to try to distinguish different modes of 

 hereditary resemblance. The characters of the two parents 

 may be blended in the offspring, or those of one parent 

 may find predominant expression (exclusive inheritance), or 

 the characters of one parent may be expressed in one part 

 of the offspring and those of the other parent in another 

 (particulate inheritance). 



Another important inquiry is into the share that the 

 various ancestors have on an average in forming any indi- 

 vidual inheritance. The inheritance of an animal repro- 

 duced in the ordinary way is always dual, partly maternal 

 and partly paternal, but through the parents there come 

 contributions from grandparents, etc. Galton's Law of 

 Ancestral Inheritance states that "The two parents con- 

 tribute between them, on the average, one half of the total 

 heritage ; the four grandparents, one quarter ; the eight 

 great-grandparents, one eighth, and so on." 



Another generalisation of great interest is Mendel's Law, 

 which seems to apply to certain cases, e.g. peas, stocks, 

 mice, and rabbits. In its simplest expression the law may 

 be stated as follows : If A be a well-established, pure-bred 

 variety with a certain character, e.g. of stature or colour, 

 and B be another well-established variety in which the 

 corresponding character is different, and if A and B are 

 crossed, the hybrid offspring (JET) will usually resemble one 

 of the parents in the particular distinguishing character. 

 The character which finds expression is called the dominant ; 

 the character which remains latent in the hybrids is called 

 the recessive. Now, if the hybrids are bred together, their 

 descendants will be of two kinds, some like the dominant 

 grandparent, some like the recessive grandparent. When 

 those like the recessive grandparent are in-bred, they yield 



