50 Dynamic Theory. 



ancient hermaphrodite nature of our prevertebrate ancestors although, 

 of course, not developed till long after their time. There are frequent 

 examples, however, of the practical use of the male mammae among 

 some of the lower mammals and occasionally among men. 



Practically, however, the male mammae are rudimentary organs 

 amongst all the higher mammals, including man. 



Instances are given of cases of reversion in which more than one pair 

 of mammae have been developed. Darwin speaks of 5 cases of men 

 who had 2 pair of the male rudimentary mammae. Also women have 

 been known with more than two pair. Two pairs of mammae are nor- 

 mal with some of the Lemur families. (Descent of Man 37.) 



The external organs of reproduction furthermore show in their devel- 

 opment their sexual differentiation from the hermaphrodite original 

 phallus or sexual protuberance of the embryo. Whether this phallus 

 develops the male or female parts, the steps are similar and the parts 

 are essentially the same in the two sexes, part for part. ( See table 

 XLIV in Haeckel's Evolution of Man.) 



The ductus venosus or venous canal has been mentioned as a deriva- 

 tive or remnant of the fifth gill arch of the embryo. In the fishes this 

 arch is permanent, and it is developed and temporarily used in the 

 mammal foetus, including man. ' ' It extends from the bifurcation or 

 forking of the umbilical vein to the vena cava inferior, into which it 

 opens below the diaphragm. At times it ends in one of the infra-he- 

 patic veins. It pours into the cava a part of the blood which passes 

 from the placenta by the umbilical vein. After birth it becomes a fibro 

 cellular cord. " ( Medical Dictionary. ) 



On the human embryo, three or four months before birth, a delicate 

 woolly covering called the lanuyo, is developed. Shortly before birth, 

 but in some cases just after birth, this wool disappears and true hair 

 grows from the same roots as the wool; sometimes the hair differs in 

 color from the wool. This wool covers all parts of the body except the 

 palms and soles, as in apes and other mammals. 



Human infants have the rudiments of 52 teeth, while adults have 

 permanently but 32. (Neil's Anatomy.) 



The tail is another rudimentary organ. In the human embryo it is 

 at first developed more rapidly than the limbs, and at one time is twice 

 as long as the hind limbs. It is then furnished with muscles which are 

 afterward re-absorbed. It does not after birth project beyond the skin 

 in man or the higher apes, except in rare cases of reversion. As al- 

 ready noted, the number of vertebrae in the adult human tail is ordin- 

 arily four, in the gibbon ( ape ) three, in the chimpanzee, gorilla and 

 orang, five, and from five to thirty-one in the tailed apes. 



These tail bones, which, in the human infant, are separated from 



