[2] He spent about eighteen months on the Amazon River and its tributaries, making collections in zoology, botany, and archaeology.

He went on another scientific expedition in 1887 to the Philippines where he made an extensive collection of birds, shells, and other natural objects.

From there he continued his journey to the Moluccas, and finally returned home by way of the Suez Canal, London, and Liverpool, after an absence of five years.

He resigned from the university in 1894 at the request of the Regents possibly because his outspoken stance on temperance had angered the local German community in Ann Arbor.

He took one final excursion in 1901, leading a group of students to the Amazon to collect specimens for the Smithsonian Institution.