MONTGOMERY, THOMAS HARRISON, JR.

(b. New York, N.Y., 5 March 1873; d. Philadelphia, Pennsylvania, 19 March 1912)

zoology.

In his brief life span of thirty-nine years Montgomery became one of the leaders in American zoology; he made substantial contributions in several fields and ranks as a major figure in one of them, cytology. He rose steadily in his profession and at his death he was professor and chairman of the department of zoology at the University of Pennsylvania.

Montgomery’s background and early life were favorable for a scholarly career. His family, which settled in New Jersey in 1701, included paternal ancestors distinguished in religion, law, and business; one of them was “the first bishop of English consecration in the United States.” Montgomery’s maternal forebears included prominent physicians and scientists: his grandfather, Samuel George Morton, was one of the founders of anthropology and served a term as president of the Academy of Natural Sciences of Philadelphia. Montgomery’s father, an insurance executive of scholarly bent, published a voluminous early history of the University of Pennsylvania, which made him an honorary doctor of letters. When Montgomery was nine years old, the family moved to a country home near West Chester, Pennsylvania; and there he developed the strong interest in natural history, particularly birds, that he maintained throughout his life.

After graduation from a private secondary school, Montgomery attended the University of Pennsylvania (1889–1891) and completed his studies at Berlin, taking his Ph.D. in 1894. At Berlin he met a group of scholars whose interest in the maturing science of cytology turned him toward the area in which he was to make his greatest contributions: the histologist F. E. Schultze; H. W. G. Waldeyer, who had published extensively on the structure of spermatozoa, on the differentiation of germ cells, and on cell division in the fertilized egg; and Oscar Hertwig, who had carried out pioneer investigations of fertilization and early development. Montgomery’s doctoral thesis, however, dealt not with cytology but with a variety of lesser problems in phytogeny, taxonomy, and anatomy. The most extensive essay was on one of the nemerteans, a subject that interested him enough to continue work on the group for many years and to publish a series of ten papers.

After returning to the United States in 1895, Montgomery served for three years as an investigator at the Wistar Institute of Anatomy in Philadelphia. He spent the summer at marine laboratories, notably at Woods Hole, Massachusetts (1897), to which he returned nearly every summer. From 1897 to 1903 he taught zoology at Pennsylvania, serving for the last three years as assistant professor. After five years as professor at the University of Texas, Montgomery was recalled to Pennsylvania in 1908 to become professor and chairman of zoology, the post he held until his death. An arduous executive achievement during this tenure was the construction of a new laboratory building. Montgomery was a coeditor of the Journal of Morphology from 1908 until his death and was president of the American Society of Zoologists in 1910.

An unusually diligent researcher who published promptly, Montgomery produced more than eighty papers between 1894 and 1912. Like many biologists of his time, he was interested in certain older problems, such as animal behavior and taxonomy, while remaining active in cytology, a more modern, laboratory-oriented field. As classified by Conklin, sixteen of his papers were devoted mainly to taxonomy, five to animal distribution, eleven to ecology and behavior, sixteen to morphology, and eight to phylogeny—in addition to twenty-five papers in cytology, on which his reputation is based.

Montgomery made a fortunate choice of animals for cell studies, working mainly on the males of the Hemiptera-Heieroptera, or true bugs, which are represented in the United States by many common, easily collected species. They are peculiarly suitable for investigating the processes of meiosis and differentiation of the spermatozoon, because the successive stages are arranged in a series of follicles along the cylindrical lobes of the testis and culminate in the mature spermatozoa, in the follicle nearest the efferent duct. In 1898 Montgomery noted that in the premeiotic, spermatogonial metaphases in the bug testis, the chromosomes consist of a definite number of pairs, many of which are individually recognizable; for example, there are often exceptionally large or small pairs. In the later maturation divisions he found that the half number of chromosomes show the same size differences. Thus, for example, if there formerly was a single large pair there now would be one large chromosome. Although not all the individual chromosomes could be followed throughout the prophase of the first maturation division, certain exceptional chromosomes did remain condensed and hence continuously recognizable. These latter he called heterochromosomes, resulting from the property of heteropycnosis.

From these observations Montgomery concluded in 1901, “Through the germinal cycle the chromosomes preserve their individuality from generation to generation—that is, a particular chromosome of one generation is represented by a particular one of the preceding, so that the chromosomes are not produced anew in each generation.” From this general conclusion he suggested that (1) the members of each chromosome pair are homologous and are of maternal and paternal origin respectively; (2) in each case the two are synaptic mates and conjugate to form a “bivalent” chromosome of the same size relative to the rest of the complement; (3) this pairing may be regarded as “the final step in the process of conjugation of the germ cells”; (4) the homologues separate at the reduction division to form the reduced number of “univalent” chromosomes; and (5) finally each spermatid receives a set of “semivalent” chromosomes, resulting from division of each univalent chromosome.

These conclusions, which contain the essentials of the chromosomal basis of biparental inheritance, were announced just prior to the rediscovery of Mendel’s laws of segregation and recombination. Montgomery himself failed to see such a possible relationship to inheritance, concluding only that the broader significance of the basic process (synapsis and subsequent separation) was that it might lead to a “rejuvenation of the chromosomes.” Despite what seems in retrospect an unimaginative and narrow interpretation, it appears undeniable that the speed with which Sutton, Wilson, and others subsequently established the correlation with the rediscovered laws of inheritance was due in large measure to Montgomery’s masterly analysis—not the least aspect of which was its clarifying terminology.

Another facet of Montgomery’s work was basic to the theory of sex determination. In certain species of bugs he noted that one chromosome, which he called the X chromosome, is single, as distinct from the paired “autosomes.” Consequently the somatic, or diploid, chromosome number is odd, and during meiosis only half the spermatids receive the X chromosome. It remained for others to point out the obvious possibility that this chromosomal mechanism could be the basis of determination of sex. Instead, Montgomery assumed that the females of these species, like the males, had the uneven chromosome number; and he became engrossed with the puzzle of how the odd number could be preserved to the next generation. Realizing that random fertilization in such a situation should also produce two evennumbered chromosomal complements with respectively one more and one less than the X type, he was led to postulate a sort of selective fertilization to maintain the odd number.

Montgomery’s other cytological contributions were not inconsiderable. In his 1901 paper he brought order to the rather chaotic views of the nucleolus by clearly distinguishing “chromatin nucleoli” (among which were the heterochromosomes) from the plasmosomes, or true nucleoli. His careful seriation of steps in the differentiation of the hemipteran spermatozoon (1911) was a model for numy later studies, including R. H. Bowen’s (1920). Noteworthy in the 1911 paper was Montgomery’s confirmation of observations on fixed material by examining cells teased out in a physiological fluid. This degree of sophistication was not attained by other ctologists for nearlv two decades.

BIBLIOGRAPHY

Montgomery’s writings include “Comparative Cytological Studies With Especial Reference to the Morphology of the Nucleolus,” in Journal of Morphology, 15 (1898), 204–265; “A Study of the Chromosomes of Germ Cells,” in Transactions of the American Philosophical Society,20 (1901), 154–236; and “The Spermatogenesis of an Hemipteron Euschistus,” in Journal of Morphology, 22 (1911), 731–799.

On his life and work, see R. H. Bowen, “Studies on Insect Spermatogenesis. I.,” in Biological Bulletin, Marine Biological Laboratory, Woods Hole, Mass., 39 (1920), 316–362; and E. G. Conklin, “Professor Thomas Harrison Montgomery, Jr.,” in Science, n.s. 38 (1913), 207–214, an excellent obituary; the complete bibliography prepared to accompany it, however, seems to have been omitted.

Arthur W. Pollister