Hylas and the Nymphs by John William Waterhouse (1896). Source: Wikipedia

Hylas

While they prepared the evening meal, Heracles went in search of a tree which would serve to make him a new oar. He uprooted an enormous fir, but when he dragged it back for trimming beside the camp fire, found that his squire Hylas had set out, an hour or two previously to fetch water from the near-by pool of Pegae, and not yet returned; Polyphemus was away, searching for him. (Hylas, Amycus and Phineus, The Greek Myths by Robert Graves, pp 589-594).

Heracles had broken his oar due to a contest he had initiated amongst The Argo’s crew to see who could row the longest, in order to speed progress with the voyage. As the Argonauts wearied, Heracles’ own oar snapped and the ship therefore put in at the mouth of the River Chius in Mysia. The disappearance of Hylas distressed Heracles mightily, because he loved the young man, whom he had spared after killing his father, King Theiodamas of the Dryopians. Heracles eventually met Polyphemus who had been unable to find hide nor hair of Hylas, except his water pitcher, abandoned at the edge of the pool of Pegae.

Unknown to the two of them, the young and beautiful Hylas had been seduced by the water-nymph Dryope and her sister-nymphs at Pegae and they had enticed the love-struck young man to come and live with them in their underwater grotto. Heracles did all he could to locate Hylas, including forcing scores of Mysians to join the search, but to no avail. He never saw Hylas again.

Eventually Jason wearied waiting for the return of Heracles, Polyphemus and Hylas and ordered the voyage to resume, although many of the Argonauts were unhappy at the decision.

Source: World History Encyclopaedia

Zagreus

ZEUS SECRETLY begot his son Zagreus on Persephone, before she was taken to the Underworld by her uncle Hades. He set Rhea’s sons, the Cretan Curetes or, some say, the Corybantes, to guard his cradle in the Idean Cave, where they leaped about him, clashing their weapons, as they had leaped about Zeus himself at Dicte. But the Titans, Zeus’ enemies, whitening themselves with gypsum until they were unrecognisable, waited until the Curetes slept. At midnight they lured Zagreus away, by offering him such childish toys as a cone, a bull-roarer, golden apples, a mirror, a knuckle-bone, and a tuft of wool. (Zagreus, The Greek Myths by Robert Graves, pp. 118-120)

Having lured the infant away from the safety of his cave and the protection of the Curetes, the vengeful Titans set about the boy. Despite Zagreus valiantly transforming into a variety of beasts to defend himself, the Titans were too numerous and too strong: they eventually overpowered Zagreus, tore him limb from limb and devoured his flesh. Athene succeeded in rescuing the boy’s heart from this carnage, enclosed it within a gypsum figure, into which she breathed immortal life. A furious Zeus later tracked the Titans down one by one, destroying them with his thunderbolts.