Board Thread:Improvements and Issues/@comment-15519592-20150125090311/@comment-5398287-20150125140456

Arrancar can be naturally formed as well, you know. They're not as powerful as they would be if created by the Hogyoku, but Hitsugaya noted this exact fact during his overview of them.

And if you'd like further proof, that very chapter showed an Arrancar begging for his life before Nnoitra cuts him down, so there's your proof.