"Croatoan" is a short story by Harlan Ellison, published in 1975 in The Magazine of Fantasy and Science Fiction, and anthologized in Strange Wine in 1978.
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The story's narrator, Gabe, is forced by a hysterical girlfriend to descend into New York City's sewers, into which he has just flushed her aborted baby. Arriving there, he finds that fetuses populate the sewers, along with an animal population composed of similarly disposed-of crocodiles, whom the fetuses ride, and the word "Croatoan", crudely lettered on a wall near the entrance to the sewer. The story ends with the narrator's hysterical realization: "I am the one they have been looking for all along....They call me father."
That sounds retarded.