The affix ḍa comes after the verb jan 'to be produced', with a past signification, when the word, in composition with it is in the Locative -7th-case.,
As उपसरे जातः = उपसरजः । जन् + ड = ज् + अ 6.4.143 = ज 'born of the first conception'; मन्दुरजः 'born in the stable'.,