Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.24

7.4.2.24

yadveva retaḥsicā upadadhāti | āṇḍau vai retaḥsicau yasya hyāṇḍau bhavataḥ sa eva retaḥ siñcati virāḍjyotiradhārayatsvarāḍjyotiradhārayaditi virāḍvahemāvāṇḍau svarāṭca tāvetajjyotirdhārayato reta eva prajāpatimeva nānopadadhāti nānā homāvāṇḍau sakṛtsādayati samānaṃ tatkaroti tasmātsamānasambandhanau te anantarhite dviyajuṣa upadadhāti yajamāno vai dviyajuranantarhitau tadyajamānādāṇḍau dadhāti

And, again, why he lays down two seed-shedders; the seed-shedders are the testicles, for only he who has testicles sheds seed. 'The wide-ruling one contained the light;--the self-ruling one contained the light,' he says; for the wide-ruling and the self-ruling ones are the testicles: they contain that light, the seed, Pragâpati. He lays them down separately, for separate are these testicles. He 'settles' them once: he thereby makes them one and the same, whence they have a common connecting-part. He lays them down close to the dviyagus (brick): the dviyagus being the Sacrificer, he thus puts the testicles together with the Sacrificer.