He wrote as readily about crocodiles as about butterflies, lancelets and lemurs. Small bony fishes, lancelets, and molluscs are infrequently consumed. By 1900 lancelets had become a model organism. Cephalochordates are represented in modern oceans by the Amphioxiformes (lancelets, also known as amphioxus). Branchiostoma is one of the few living genera of lancelets (order Amphioxiformes). TMEM81 orthologs have not been detected among agnatha, lancelets, tunicates, or invertebrates. The evolution of TBR1 has been studied in amphioxi, also known as lancelets. Lancelets, which are primitive chordates, possess only one homologue of "Drosophila" "Hh" (figure 7). For example, the gill-slits of lancelets are used for feeding only, and not for respiration. In Asia, lancelets are harvested commercially as food for humans and domesticated animals. Lancelets are gonochoric animals, i.e. having two sexes, and reproduce via external fertilization.