138 THE HORSE. 
5. Tue Ovum consists of the germ-cell, intended to form part of the 
embryo,—and of the yolk, which nourishes »poth, until the vessels of the 
mother take upon themselves the task; or, in oviparous animals, till 
hatching takes place, and external food is to be obtained. ‘The ovum is 
tarried down by the contractile power of the fallopian tubes from the 
ovary to the uterus, and hence it does not require automatic particles ike 
the semen. 
6. Tur Empryo, or young animal, is the result of the contact of the 
semen with the ovwm, immediately after which the sperm-cell of the former 
is absorbed into the germ-cell of the latter. Upon this: a tendency to 
increase or “ grow” is established and supported at first, by the nutriment 
contained in the yolk of the ovum, until the embryo has attached itself to 
the walls of the uterus, from which it afterwards absorbs its nourishment 
by the intervention of the placenta. 
7. As THE Mane anp Fematr each furnish their quota to the forma- 
tion of the embryo, it is reasonable to expect that each shall be repre- 
sented in it, which is found to be the case in nature; but as the food of 
the embryo entirely depends upon the mother, it may be expected that 
the health of the offspring and its constitutional powers will be more in 
accordance with her state than with that of the father; yet since the sire 
furnishes one-half of the original germ, it is not surprising that in exter- 
nals and general character there is retained a fac-simile, to a certain 
extent, of him. 
8. Ton Ovum or Mammatta differs from that of birds chiefly in the 
greater size of the yolk of the latter, because in them this body is intended 
to support the growth of the embryo from the time of the full formation ~ 
of the egg until the period of hatching. On the other hand, in mammalia 
the placenta conveys nourishment from the internal surface of the uterus 
to the embryo during the whole time which elapses between the entrance 
of the ovum into the uterus and its birth. This period embraces nearly 
the whole of the interval between conception and birth, and is called 
utero-gestation. 
9. In auL THE MaMmMALIA THERE IS A PeriopicaL “ Heat,” marked by 
certain discharges in the female, and sometimes by other remarkable 
symptoms in the male (as in the rutting of the deer). In the former it is 
accompanied in all healthy subjects by the descent of an ovum or ova into 
the uterus; and in both there is a strong desire for sexual intercourse, 
which never takes place at other times in them (with the single exception 
of the genus Dimana). 
10. THE Semen retains its fructifyimg power for some days, if it is con- 
tained within the walls of the uterus or vagina, but soon ceases to be 
fruitful if kept in any other vessel. Hence, although the latter part of 
the time of heat is the best for the union of the sexes, beeause then the 
ovum is ready for the contact with the semen, yet if the semen reaches 
the uterus first, it will still cause a fruitful impregnation, because it 
remains there (or in the fallopian tubes) uninjured until the descent of 
the ovum. 
11. Tar INFLUENCE OF THE MALE upon the embryo is partly dependent 
upon the fact, that he furnishes a portion of its substance in the shape of 
the sperm-cell, but also in great measure upon the effect exerted upon the 
nervous system of the mother by him. Hence, the preponderance of one 
or other of the parents will, in great measure, depend upon the greater or 
less strength of nervous system in each. No general law is known by 
which this can be measured, nor is anything known of the laws which 
