Well, we do know that Zoanoids crossbred with humans in the past. So that is my understanding as to why they all have genitals and depicted lack of them in the manga is due to artistic and Japanese laws. Though you are right, Salkafar, in that since there is a lack of actual appearance of the, we can't back it up as a fact, however, you can understand the basic reasoning as to why they likely have them. Chronos would like nothing more than to have as many Zoanoids as possible, and removing their ability to reproduce would of course limit that goal, not to mention cause serious problems in the event of a war, such as targeting none Zoanoid populations in order to bring the species into extinction, if you build a strategy around killing base humans and avoiding combat with Zoanoid units, you pretty much have a fast win. It's the same principal as targeting supplies. Wipe those out and your army can't feed. resupply, or replace units. If the Advents with all their brilliant thought for war, would overlook something that simple in billions of years, than they deserve to get wiped out by Humanity!