Most part of given concerning the reproduction and e development of cetaceans concerned in sort formerly hunted(formerly chased away) for the commercial and economic value They were taken in by the researchers attached to vessels and to whalers' stations as well as to museums which were dedicated to them. More recently, specimens of sorts killed accidentally during fishing years dedicated to the other navy creatures widened the field of investigation of the scientists. So, we estimate(esteem) at more than a million the number of dolphins(dauphins) with long beak and speckled dolphins(dauphins) (kind(genre) Stenella) who drowned themselves in the nets of thonniers. "Spiders" (nets with stitches ténues) spread(displayed) near coasts charged a heavy levy in the cetaceans of small size which evolve in little deep waters.

THE SEXUAL DIMORPHISME

During the adaptation to the aquatic life, the dock of the body of cetaceans implied the modification of their external genitalia. Flooded in the mass of the body, they are difficult to distinguish: the penis of males(mates) is maintained in one preflea(prechip) (except during the erection) the opening of which is in crack (said genital crack) of aspect similar to the vulva of females. The most marked difference between both sexes is the distance which separates the genital crack of the anus: she(it) represents some 10 percent of the length of the body to males(mates) while the vulva seems to prolong the anus to female. The mammary glands of females are hardly visible: both nipples are arranged in the other cracks situated by part and the others of the genital crack. They go out of it only during the feeding. Glands itself are flooded under the bacon and hide a wide portion of the wall ventrale; Their swelling guesses only to females producing a lot of milk.

There is nevertheless a sexual dimorphisme to the grown-up specimens of some sorts. So, the size of males(mates) is more raised(more brought up) than that of their partners to sperm whales (Physeter catodon), globicéphales (kind(genre) Globicephala) and the killer whales (Orcinus orca). The males(mates) of these last ones possess besides a more impressive dorsal aileron. But, contrary to certain ground mammals, the sexual dimorphisme does not concern either the livery or the shape of the body.

The picture(table) gives, for some sorts of dolphins(dauphins), certain likely data concerning the first phases of their existence, and also their rough longevity.

The observations made in océanariums on Tursiops allowed to notice that, during the parturition, the young person appears by the caudal region, that the umbilical cord breaks spontaneously and that the mother hurries to lead the newborn child towards the surface so that he can take his first breath as quickly as possible. It is an indispensable operation, dices there his(her,its) exit(release) of the womb, small dolphin(dauphin) tends to flow, its lungs still not containing air(sight). It is very frequent that another female comes to help the mother to bring to the foreground the young person, who is tall (approximately a third(third party) of the total length of the grown-up female).

At dolphins(dauphins), as at all the Cetaceans generally, the maternal instinct is very developed, and the mother stays up attentively her shoot, always ready to defend(forbid) him(it) furiously against any attack. The sucking of the young Cetaceans is known for a long time: the nipples of the mother, situated by pair on both sides of the sexual opening, are provided with muscles powerful allow to throw(launch) a jet of milk in the mouth of the infant. In the mouth of the infant. Certain young dolphins(dauphins) content themselves, until the total weaning, with this milk diet. Others begin, before the end of the period of feeding, to chase small fishes; but it is that from the age from five to seven months that they can arrest them effectively, that is when their teeth drilled(leaked out), this one allowing them then to hold(retain) preys. According to the sorts, the period of feeding can last of some months for two. The growth is very fast, because the milk of cetaceans is exceptionally rich in fats (35 in 40 %). The sexual maturity, to a female of Tursiops been born in captivity, was reached(affected) at the age of six. We consider that the females of dolphins(dauphins) common are pubères at about three years; males(mates) one the year later. For globicéphales, the corresponding times are six-seven years to females and twelve years old to males(mates).