Montgomery returned to America in early 1895 and spent three years as a researcher at the
Wistar Institute in Philadelphia. During this period he spent consecutive summers working with
Alexander Agassiz at his Rhode Island laboratory, the University of Pennsylvania marine laboratory at
Sea Isle City, New Jersey, and at the
Marine Biological Laboratory at Woods Hole, Massachusetts; the latter to which he would return nearly every summer for the rest of his life. In 1897 he joined the faculty of the University of Pennsylvania where he worked until 1903, then was professor at the
University of Texas from 1903 to 1908 until returning to Pennsylvania where he worked as head of the zoology department until his death in 1912. He was a member of the
American Society of Zoologists (president in 1910),
American Association for the Advancement of Science,
American Society of Naturalists,
American Philosophical Society,
Academy of Natural Sciences of Philadelphia, and the Texas Academy of Science (president in 1905). He was co-editor of the
Journal of Morphology from 1908 to 1912.
Cytology '', a ribbon worm Harrison published 25 papers on
cell biology, primarily using insect cells. His most notable research includes early observations of the pairing of maternal and paternal
chromosomes during cell division. He was first to propose that chromosomes play the dominant role in sex determination, although he rejected the idea that sex was determined by chromosomes alone, and some historians claim he was the first to propose the
chromosome theory of inheritance, an idea widely credited to
Walter Sutton and
Theodor Boveri. He also detailed the morphology of the
nucleolus, and observed that in some
hemipteran insects the
germ cells of males but not females contain odd numbers of chromosomes, which is now known to influence sex-determination,
Worms, spiders, and other invertebrates Montgomery's earliest papers concerned
ribbon worms (phylum Nemertea), a group on which he would write 10 papers. He also published 10 papers on
horsehair worms (phylum Nematomorpha) and two on
rotifers. Montgomery wrote 14 scientific articles on
spiders, and he was known to keep large amounts in his laboratory and home from which he recorded observations of courtship, mating, and other behaviors. He wrote on the taxonomy of
wolf spiders (family Lycosidae),
lynx spiders (Oxyopidae), and
nursery web spiders (Pisauridae). In a 1909 paper detailing the anatomy and development of various organs in spiders he rejected a prevalent idea at the time that arachnids evolved from Merostomata (a now obsolete group including
horseshoe crabs and the extinct
eurypterids) adapting to a terrestrial life, and proposed instead that the aquatic lifestyle of horseshoe crabs evolved from terrestrial ancestors. His collection consisted of 145 species collected from 1885 to 1891, and again from 1895 to 1897. Montgomery is known for proposing the hypothesis that migratory behavior is negatively correlated with rates of evolutionary diversification, now known as "Montgomery's Rule". He published original research on the diet and foraging ecology of
Long-eared Owl (
Asio otus) and
Short-eared Owl (
A. flammeus). His book
The Protection of Our Native Birds (1906) was an important early contribution to the bird conservation movement.
Other works Montgomery also published on a variety of other topics including principles of animal classification and larval development of the
red-backed salamander. His 1908 book,
The Analysis of Racial Descent in Animals, described his ideas of classification. He contributed articles to
Popular Science Monthly, and also published a memoir of his father in 1905. == Death ==