However, [Franz] Steindachner (1875), in describing Arius planiceps, a catfish from Panama, found that at the breeding season the innermost edges of the ventral fins of the female are developed so as to form a kind of pocket. He conjectured that the eggs are extruded into this, fertilized by the male, and then taken into his mouth. He found a similar structure on the female of A. kessleri, the male of which is also a mouth brooder.