Summary 1. The action of the gene on characters an animal is limited to those manifestations which are physiologically possible if survive. Environmental conditions affecting physiology will therefore have a selective genes give rise in harmony with environment concerned. main problem breeding be able direct course evolution and select giving increased development certain characters. 2. Where character by environmental it not for capacity manifesting themselves excess these limitations. If,...

ABSTRACT Methods and experiments are described for testing the length of fertility sperms in male female tracts rabbits. The may retain their tract up to 38 days, but only 30 hours. In cases where had remained 24-30 hours before ovulation small litters were frequently produced; it is suggested that this due end point vitality falling within limits time during which process occurs. bearing these results on problems sterility discussed.

ABSTRACT By matings with fertile bucks at different intervals of time after a mating vasectomised buck (to induce ovulation) the insemination in rabbit can be moved successively nearer to, at, and ovulation. From inseminations 5 hours before to 2 ovulation percentage which are fertile, average litter size, number young per fall gradually constant rate until absolute sterility is obtained. Does produce large litters when mated normally (10 may made small by shortly or The ova only capable...

I n a previous paper (1) some of the factors which control fertility in domestic animals were discussed. These for purposes clearness investigation divided into two groups: The number eggs shed; and (2) develop to reach birth size. By this means way various affect could be determined, example, it was shown that effect age on fertility, literature has been reviewed by Harris (2), is due shed at each oestrus period. Young sows examined had average 14 corpora lutea ovaries while old 20 lutea.

After a consideration of the ways in which fertility domestic animals is controlled some factors limit it have been investigated. Various circumstances control number ova shed at each heat period. Data are presented show that low young as compared with adult sows due to fact not so many Counts made corpora lutea present ovaries and foetuses uteri pregnant rabbits pigs. The results more period than produced birth. Some possibly may be lost but after fertilization atrophy their development...

The ferret has been but little used for experimental laboratory work on reproduction, although its small size and marked sexual changes, together with the fact that it ovulates only after coitus, make a very suitable species investigations. study of ferret's œstrous cycle, however, formed subject an investigation by one us some 25 years ago (Marshall, 1904), when was shown there normally well-marked breeding season, extending from about March to August, anœstrum during rest they year....

The secretions of the cervix are interest because changes that occur in them during oestrous cycle and pregnancy. It is probable these have an efEect assisting or hindering ascent spermatozoa to Fallopian tubes after their deposition vagina.

1. Injection of pituitary extract has an immediate action on milk secretion, but the effect soon passes off. During period after injection there is a rather rapid decrease in milk‐flow, this gradual and no sudden drop followed by increasing secretion to normal. This indicates that not muscular. 2. From result successive injections at various intervals as well from numerous other observations it also concluded 3. The daily yield only slightly increased injection. shows acts setting free than...

An investigation was carried out to determine the extent of maternal influence on size calves at birth and during subsequent stages growth, by making reciprocal matings between large South Devon small Dexter cattle. As a preliminary experimental results, data concerning respective parent breeds were analysed. From first part study following information obtained: 1. The mean weight purebred 100·3 ± 1·47 lb. with tendency, though not statistically significant, for male be heavier. Calves born...

Recent experimental work has resulted in proving that there is a definite functional correlation between the growth of corpora lutea ovaries and hypertrophy mammary glands (Ancel Bouin O’Donoghue). In present paper experiments are described showing this rabbits have never been pregnant may be so considerable as to lead production milk, secretion which temporarily increased by injection pituitary extract. Further recorded uterus not necessary factor development gland. The influence...

The parts played by the various reproductive organs in causing growth of mammary gland and secretion milk have been subject much recent investigation. Most work has done with rabbit, changes which occur its glands studied very minutely. causes during first part pregnancy are now conclusively shown to be due influence corpus luteum. These rabbit culminate at about 16th day after coitus; this time pseudo-pregnant rabbits ( i. e ., had coitus developed corpora lutea, but not become pregnant)...

Records of the live and carcase weights sheep exhibited at Smithfield Show from 1893 to 1913 have been treated statistically. The results show average weights, rates growth, proportions in different breeds 9 months 21 age (see Tables II V). On all rate growth declines 4·7 lbs. per week birth 1·7 age. percentage increases with on 61 cent, 65 it fat 5·7 64 months. other hand pluck, skin alimentary canal (“Unaccounted for”) decrease Ratios early maturity are given for various factors which...

In order to disentangle the various causes affecting foetal growth, and so birth weight of animal, it is necessary employ statistical methods in addition physiological ones. This paper presents suited a study growth where two such factors have be separated their effects on measured quantitively.

The mares chosen for the investigation of changes in reproductive organs during oestrous cycle were kept under observation some time before they killed. duration heat period these animals was 7 days and length dioestrus 16 days. Ovulation takes place at about a day end oestrus. size ovary is chiefly influenced by growing Graafian follicle. number follicles present different stages varies greatly. numerous small beginning oestrus disappear later cycle; it suggested that this may be due to...

Weights and measurements of sides bacon made under standard conditions from different breeds crosses pigs exhibited at the London Dairy Show 1922–31 have been analysed statistically. 1. The actual live weight pig affects carcass percentage more than does breed or type. 2. For a 200 lb. weight, there is an optimum (about 79 per cent) 58 cent). highest not necessarily best, for below about this level proportion bone will be too large above fat large. 3. reasons why certain proportions are...