Note 152 — Chapter X
William Johnston translation
The Amphisbæna of the system has not two heads, but is of equal thickness at the head and tail; so that it appears as if it could advance both ways. There are, however, real two-headed snakes; at any rate, some of that kind have been seen in America. This monstrosity is perhaps transmitted by generation, as the monstra per excessum in the families of Ruhe and Calleja, whose descendants have more than five fingers and toes. It can be determined only by accurate anatomical and physiological examination, whether these two-headed snakes form a particular genus. F.