Complex sentence: Taking up embryology, he went to the United States to investigate the development of 'Balanoglossus' an informal name for the worm-like enteropneust hemichordate Saccoglossus kowalevskii Agassiz, 1873 which led to his interest in vertebrate origins.
Split into simpler sentences: Taking up embryology, he went to the United States to investigate the development of "Balanoglossus". This worm-like enteropneust hemichordate led to his interest in vertebrate origins.