i88 E VOL UTION AND DISEASE. 



of an individual are in many instances transmitted to 

 the offspring. Malformations, as such defects are called, 

 arising in this manner are usually classed as arrests of 

 development, and as it is clearly established that the 

 embryological history of a complex individual may be 

 regarded as an abbreviated history of its evolution, it 

 necessarily follows that, should the development of a 

 part be arrested at any particular stage, we should 

 expect to find, in some less specialized mammal, this 

 stage represented as a permanent condition. For 

 instance, children are often born with club feet ; the 

 commonest congenital form is that which in the sole of 

 the foot looks inwards and upwards, and the heel is 

 slightly raised (talipes equino-varus). In the child 

 before it is born the feet are for several months in this 

 position, and gradually pass into that assumed normally 

 in the adult. Not infrequently the foot fails to assume 

 a position at right angles to the leg, and malformation 

 is the result. Now it is very instructive to remember 

 that the orang's foot is in the position typical of talipes 

 equino-varus, and this is not limited merely to the 

 position of the foot, but extends also to the disposition 

 of the articular surfaces on the ankle-bone. 



It is far from my intention to enter in a detailed 

 manner into all forms of malformation which may be 

 transmitted ; that such characters are inherited is in- 

 disputable, but it may be useful to describe an instance 

 in which it has been possible to produce a permanent 

 variety in which the existence of a malformation is the 

 distinguishing feature. This is the more important 

 because as a rule defects of this class appear sporadically 



