Reference for Bekhorot 111:20

לקח עשרה עוברים במעי אמן כולן נכנסין לדיר להתעשר

[To revert to] the [above] text: R'Assi reported in the name of R'Johanan: If one bought ten embryos which were in the insides of their mothers, all of them enter the shed to be tithed'.

Jastrow