g^5 COMPARATIVE HISTORICAL. 



bv Lamarck 1809, or the doctrine of the " Unity of the Animal Kingdom," corresponding to 

 the ancient view of Empedocles, that all species of animals were derived by variations from a 

 few fundamental forms; that at first there were only a few lower forms from which the 

 numerous si>ecies were developed a view supported by Geoffrey St Hilaire and Goethe. After 

 a long period this view was restated and elucidated in the most brilliant and most fruitful 

 manner by Charles Darwin in his " Origin of Species " (1859) and other works. He attempted 

 to show how modifications may be brought about by uniform and varying conditions acting for 

 a long tame. Amongst created beings each one struggles with its neighbour, so that there is a 

 real "straggle for existence. " Many qualities, such as vigour, rapidity, colour, reproductive 

 activitv, &c, are hereditary, so that in this way by "natural selection" there may be a 

 gradual improvement, and therewith a gradual change of the species. In addition, organisms 

 can, within certain limits, accommodate themselves to their surroundings or environment. Thus 

 certain useful organs or parts may undergo development, while inactive or useless parts may 

 undergo r et rogression, and form " rudimentary organs." This process of "natural selection, ' 

 causing gradual changes in the form of organisms, finds its counterpart in "artificial selection " 

 amongst plants and animals. Breeders of animals, for example, by selecting the proper crosses, 

 can within a relatively short time produce very material alterations in the form and characters 

 of the animals which they breed, the changes being more pronounced than many of those 

 that separate well-defined species. But, just as with artificial selectiou, there is sometimes a 

 sudden "reversion" to a former type, so in the development of species by natural selection 

 there is sometimes a condition of atavism. Obviously, a wide distribution of one species in 

 different climates must increase the liability to change, as very different conditions of environ- 

 ment come into play. Thus, the migration of organisms may gradually lead to a change of 

 species. 



Biological Law. Without discussing the development of different organisms, we may refer 

 to the "fundamental biological law " of Haeckel, viz., " that the ontogeny is a short repetition 

 of the phylogeny," [ontogeny being the history of the development of single beings, or of the 

 individual from the ovum onwards, while phylogeny is the history of the development of a 

 whole stock of organisms, from the lowest forms of the series upwards] (p. xxxv). When applied 

 to man, this law asserts that the individual stages in the course of the development ot the 

 human embryo, e.g., its existence as a unicellular ovum, as a group of cells after complete 

 cleavage, as a blastodermic vesicle, as an organism without a body-cavity, &c. ; that these 

 stages of development indicate or represent so many animal forms, through which the human 

 sixties in the course of untold ages has been gradually evolved. The individual stages which 

 the human race has passed in this process of evolution are rapidly rehearsed in its embryonic 

 development. This conception has not passed without challenge. In any case, the comparison 

 of the human development and its individual organs with the corresponding perfect organs of 

 lower vertebrates is of great importance. Thus, a mammal during the development of its 

 organs is originally possessed of the tubular heart, the branchial clefts, the undeveloped brain, 

 the cartilagiuous chorda dorsalis, and many arrangements of the vascular system, &c), which 

 are permanent throughout the life of the lowest vertebrates. These incomplete stages are per- 

 fected in the ascending classes of vertebrates. Still, there are many difficulties to contend with 

 in establishing both the evolution hypothesis of Darwin and the biological law of Haeckel. 



Historical. Although the impetus to the study of the history of development has been most 

 stimulated in recent times, the ancient philosophers held distinct but very varied views on the 

 question of development. Passing over the views of Pythagoras (550 B.C.) and Anaxagoras 

 (500 b.c), Empedocles (473 B.C.) taught that the embryo was nourished through the 

 umbilicus ; while he named the chorion and amnion. Hippocrates observed incubated eggs 

 from day to day, noticed that the allantois protruded through the umbilicus, and observed that 

 the chick escaped from the egg on the 20th day. He taught that a 7 months' foetus was viable, 

 and explained the possibility of superfoetation from the horns of the uterus. The writings of 

 Aristotle (born 384 b.c.) contain many references to development, and many of them are 

 already referred to in the text. He taught that the embryo receives its vascular supply 

 through the umbilical vessels, and that the placenta sucked the blood from the vascular uterus 

 like the rootlets of a tree absorbing moisture. He distinguished the polycotyledonary from the 

 diffuse placenta ; and he referred the former to animals without a complete row of teeth in both 

 jaws. In the incubated egg of the chick he distinguished the blood-vessels of the umbilical 

 vesicle, which carried food from the cavity of the latter, and also the allantois. He also 

 observed that the head of the chick lay on its right leg, and that the umbilical sac was ulti- 

 mately absorbed into the body. The formation of double monsters he ascribed to the union of 

 two germs or two embryos lying near each other. During generation the female produces the 

 matter, the male the principle which gives it form ana motion. Thei-e are also numerous 

 references to reproduction in the lower animals. Erasistratus (304 B.C.) described the embryo 

 as arising by new formations in the ovum Epigenesis, while his contemporary, Herophilus, 

 found that the pregnant uterus was closed. He was aware of the glandular nature of the 

 prostate, and named the vesicuhe seniinalis and the epididymus. Galen (131-203 a.d.) was 

 acquainted with the existence of the foramen ovale, and the course of the blood in the foetus 



