Philo Judaeus De Virtutibus 138

[138] for if animals, which grow and increase like plants, and which are considered to be as it were parts of the mothers which have conceived them, being still united to them, and being destined hereafter, after an appointed period of months, to be separated from the close connection to which they are at present attached, are, because of the hope that at some future time they may become living creatures, preserved at present by the safety thus guaranteed to their mothers, in order that the aforesaid pollution may not come to pass; how can it be that the animals, when brought forth, shall not be preserved in a still greater degree, which in their own proper persons have received the gift of life and body? for it is the most impious of all customs, to slay both offspring and mother at one time and on one day.