Shanti Parva 214.23

The great and divine Rishi Atri is a inaster of the subject of the generation of the vital secd. The juices that are produced by food, the passage called Manovaha, and the desire that is born of imagination,-these three are the causes which create the seminal fluid which has Indra for its presiding god. The passion that helps the passing out of this fluid is, therefore, called Indriya.