As to all mammals, the growth rate of the foetus is maximal at the end of the period of gestation. He(it) is almost improbable at the big cetaceans. Judge it: during the last two months of the gestation, the weight of the foetus of a blue rorqual increases by two tons, is some hundred kilos a day just before put low. This rate exceeds the rate of all other cetaceans; it is 10 times as raised(brought up) that that of the ground mammals and from 500 to 1000 times bigger than that of a human foetus. Contrary to what takes place at mammals living on the ferle earth(ground), the variation of size in the birth observed between the different sorts of mysticètes and odontocètes is not due to differences of period of gestation, but indeed to different foetal growth rates.

Capable now of estimating(esteeming) the age of a cetacean, we can calculate the growth rate after the birth. To all the maritime mammals, the development of the newborn child is extremely fast (so fast what is more it is possible to determine the age of the young person according to its length, until one year at least). The maternal milk is indeed particularly rich in fats and, in a lesser measure, in proteins. An animal of two years can so be also big (otherwise bigger) as another five-year-old old man. Before the weaning (which(who) takes place at about seven months), a rorqual young person blue will have seen growing his weight of about 17 tons, that is 80 kg a day. If his(her,its) size is 8 m in the birth, she can have doubled at the age of two.