COMPARATIVE. HISTORICAL. 1005 



a coelom, etc., indicate an equal number of animal varieties, from which the human 

 race, in the course of inconceivable time, has gradually evolved. The separate 

 steps through which the human race has passed in the process of transformation 

 have been briefly repeated in its embryonal development. This exposition has, 

 naturally, not escaped criticism. In any event, the comparison of human de- 

 velopment with relation to the individual organs with the corresponding fully 

 developed organs of the vertebrates is important. Thus also mammals possess 

 in the development of their organs, originally, the simple heart, the visceral 

 clefts, the undeveloped rudimentary brain, the cartilaginous chorda dorsalis, 

 various arrangements of the vascular system, etc., that are peculiar to the lowest 

 forms of vertebrates throughout life. In the higher classes, these incomplete 

 rudimentary structures gradually approach perfection. The morphological 

 differences between man and the gorilla or the chimpanzee are slighter than those 

 between the anthropoids mentioned and other apes. The fossil Pithecanthropus 

 erectus was at first regarded as an extinct link between anthropoids and man, 

 but recently more correctly as a powerful long-armed ape (hylobates, gibbon) ; 

 the Palasopithecus sivalensis may occupy an analogous position, with its cranial 

 cavity two-thirds the size of the human cranial cavity and occupying an inter- 

 mediate position between the cranial cavity of the anthropoids and the lower 

 races of man. In detail, however, there are still many difficulties in the way of 

 establishing the Darwinian theory and the fundamental biogenetic law. 



Historical. Although the discoveries in embryology, more than those in any 

 other branch of biological science, belong especially to'modern times, it is, never- 

 theless, interesting to consider the views of the ancients upon different points. 

 Pythagoras (550 B. C.) rejected the theory of spontaneous generation: All 

 life results from seed. According to Alkmaeon (580 B. C.) both sexes furnish 

 the fecundating material; the sex of the offspring corresponds to the sex supply- 

 ing the most seed. In development the head is formed first. Anaxagoras (500 

 B. C.) believed that boys came from the right and girls from the left sexual gland. 

 Empedocles (473 B.C.) recognized the nutrition of the embryo through the um- 

 bilicus; he was the first to designate the chorion and the amnion, and the segmen- 

 tation of an embryo as complete on the thirty-sixth day. He taught that the 

 first animals of creation were the most incomplete. Hippocrates considered 

 the seventieth day the earliest time for movement and the two hundred and 

 tenth day as term. He taught, with Democritus, that the sexual material 

 came together from all parts of the body (Darwin's pangenesis), thus accounting 

 for the resemblance of the offspring. He observed incubating eggs from day to 

 clay, and saw in them the allantois emerge from the umbilicus, and the chick 

 escape on the twentieth day. He taught that seven-month children are viable, 

 explained the possibility of superfetation from the horns of the uterus and de- 

 scribed the lithopedion. According to Plato (430 B. C.) the spinal cord is formed 

 first, as the appendix of which, the brain appears anteriorly. The writings of 

 Aristotle (born 384 B. C.) are rich in observations of which many have already 

 been cited in the text. He taught that the embryo received its blood-supply 

 through the vessels of the umbilical cord, and that the placenta absorbs blood 

 from the vascular uterus, as a tree absorbs moisture through its roots. He differen- 

 tiated the polycotyledonaryand the diffuse placenta; he attributed the former to ani- 

 mals that do not have complete rows of teeth in both jaws. In the incubated 

 bird's egg he recognized the vessels of the yolk-sac, which convey nourishment 

 from the latter to the embryo, and the vessels of the allantois. The statement is 

 correct also that the chick rests with its head on the right leg, and that the yolk- 

 sac finally enters the body. In the birth of mammals when the head alone is 

 born it does not breathe. The formation of double monsters is ascribed to the 

 junction of two germs or two embryos lying in close proximity. In the process 

 of conception, the female supplies the material, the male the principle that is 

 responsible for form and movement. With regard to reproduction in the lower 

 animals, reference may be made to the generative arm of the cephalopods, the 

 yolk-sac of the cuttle-fish, the yolk-sac placenta of the smooth shark, the con- 

 jugation of snakes and the absence of the amnion and the allantois in fish and 

 amphibia. Diocles (a contemporary of Theophrastus, born 371 B. C.) appears 

 to have seen the ovum as early as the second week as a cutaneous vesicle, marked 

 by bloody points (villi ?) ; he describes also the cotyledons of the uterus. Erasist- 

 ratus (304 B. C.) taught the development of the embryo by a neoplastic process 

 in the ovum (epigenesis) ; he considered scar- formation in the uterus as a cause for 

 sterility. His contemporary Herophilus found that the pregnant uterus is closed. 



