Beneden, Edouard Van

Beneden, Edouard Van

(b. Louvain, Belgium, 5 March 1846; d. Liège, Belgium, 28 April (1910)

zoology, embryology.

Van Beneden’s father, the zoologist P.J. Van Beneden, was professor at the Catholic University in Louvain. Edouard was appointed professor at the University of Liège in 1870 with the qualification of chargé de cours and was promoted to ordinarius in 1874.

His scientific work is characterized by a great unity resulting from the character of the problems to which he devoted his attention. In 1872 Van Beneden went to Brazil, and from there he brought back a number of specimens, particularly Annelida, which were studied by Armauer Hansen. P.J. Van Beneden had organized a modest laboratory on the Belgian seacoast at Ostend, and there Edouard had the opportunity to collect and study many specimens of fauna, particularly from Thornton Bank, near Ostend. His main interests at that time were directed toward the animal groups his father had studied: protozoa, hydraria, cestodes, nematodes, and tunicates. He soon extended these studies to dicyemida, and later to vertebrates, particularly mammals.

In a paper on the origin of the sexual cells of hydroids (1874), Van Beneden showed, besides great care in observation, his tendency to sometimes bold generalization. At that time, the gastrula theory of metazoan development was presented by Huxley, Lankester, and Haeckel; Van Beneden suggested that ectoderm and endoderm have opposed sexual significance, the ectoderm being the male layer and the endoderm the female layer. He thereafter recognized the hermaphrodite nature of the egg, an idea he later developed in his studies on cestodes.

Van Beneden’s first publication on dicyemida dates from 1876. He made a thorough and careful study of their structure and observed that they derive from an epibolic gastrula, the hypoblast of which is formed by a long, central single cell. In 1877 he proposed the creation of the phylum Mesozoa, considering it an ideal transition between monocellular and multicellular animal forms. This idea, after a temporary eclipse, has regained popularity.

In 1864, by the application of the embryogenetic method and the biogenetic law, Kovalevski had shown to everyone’s surprise, that tunicates were chordates. They therefore were excellent material for studies in comparative morphology, with a view to establishing their phylogenetic relations with other animals. In collaboration with his colleague Charles Julin, Van Beneden showed, in a contribution to ascidian embryology that represents one of the first and best works on the segmentation of the egg, that the germ in formation shows a bilateral symmetry and a clear polarity. In 1884 Van Beneden and Julin were the first to follow, in a strictly bilateral egg, what is now called cell lineage.

In 1887, Van Beneden and Julin published an important paper on tunicate morphology in which they stated that the mesoblast derives from the enterocele. They also accepted that the cardiopericardic vesicle and the epicardia derive from common forms, the procardia, which they considered to be pharyngeal diverticula.

Van Beneden pursued these studies until his death and left notes that have been published by his disciple Marc de Selys-Longchamps, who, from drawings left by his master, concluded that the endoblast is not derived from the enterocele and showed that the pericardium of tunicates is the ultimate remainder of the chordate celom.

Van Beneden’s most famous contributions to science are his papers on the maturation and fertilization of the egg of Ascaris megalocephala, the first of which was published in 1883. In this paper he revealed the essential nature of fertilization: the union of two half-nuclei, one female and the other male. He showed that in Ascaris, it is not until the male and female pronuclei have formed what we now call chromosomes (which are accurately represented in his plates) that the respective nuclear membranes break down. He described how each set of chromosomes moves to the equatorial plate. Van Beneden saw that in the variety of Ascaris he called univalens, which had only two chromosomes, each parent contributes one chromosome to the pair found in the zygote. Through this discovery, the individuality of the single chromosome was first demonstrated.

In bivalens (the variety with four chromosomes in the fertilized egg) Van Beneden showed the presence of two chromosomes in each of the pronuclei, and of four in the zygote. He also discovered that in giving off the polar bodies, the number of chromosomes within the egg nucleus is reduced from four to two.

Van Beneden’s opinion on the mechanism of karyogamic reduction, which he had discovered, was that of the four chromosomes of bivalens, two entered the first polar body and two remained to form the female pronucleus. It was shown independently, by Theodor Boveri in 1887–1888, and by Oscar Hertwig in 1890, that the real nature of the “maturation” division leading to the formation of ripe gametes in both sexes is that each chromosome in the mother cell divides once, while the cell itself divides twice. In 1892 Boveri showed, in Ascaris megalocephala bivalens, that two of the eight daughter chromosomes of the egg’s mother cell go into each of four cells: into each of the three polar bodies (if the first polar body divides after being given off) and into the ovum.

In a paper published in collaboration with the photographer Neyt (1887), Van Beneden described the centrosome and showed that it was a permanent cell organ which remained in the cell during the resting period and divided into two parts before the beginning of the next mitosis.

From the beginning of his scientific work, Van Beneden had been preoccupied with the problem of the origin of vertebrates. His first interpretation of the didermic mammalian embryo was immediately accepted, but in 1888 he concluded a study of the gastrulation of mammals that became a classic only after his death.

BIBLIOGRAPHY

1. Original Works. A complete list of Van Beneden’s publications is in A. Brachet, “Notice sur Edouard Van Beneden,” in Annuaire de I ’Académie royale de Belgique,89 (1923), 167–242, The most important of his works are “De la distinction originelle du testicule et de I’ovaire, Caractère sexuel des deux feuillets primordiaux de I’embryon, Hermaphrodisme morphologique de toute individualité animale, Essai d’une theéorie de la fécondation.” in Bulletin de I’Académie royale de Belgique. Classe des sciences, 2nd ser,. 37 (1874), 530–595; “Recherches sur les dicyémides, survivants actuels d’un embranchement des mésozoaires,” ibid., 41 (1876), 1160–1205; 42 (1876). 35–97; “L’appareil sexuel femelle de I’ascaride mégalocéphale,” in Archives de biologie, 4 (1883), 95–142; “La segmentation chez les ascidiens dans ses rapports avec I’organisation de la larve,” in Bulletin de I’Académie royale de Belgique, Classe des sciences, 3rd ser., 7 (1884), 431–447, written with C. Julin; “La segmentation chez les ascidiens et ses rapports avec I’organisation de la larve,” in Archives de biologie,5 (1884) 111–126, written with C. Julin; “Nouvelles recherches sur la fécondation et la division mitosique chez I’ascaride mégalocéphale, Communication préliminaire,” in Bulletin de I’Académie royale de Belgique, Classe des sciences, 3rd ser,. 14 (1887), 215–295, written with A, Neyt: and “Recherches sur la morphologie des tuniciers,” in Archives de biologie,6 (1887). 237–476, written with c. Julin,

II, Secondary Literature. The best biography of Van Beneden is the one by Brachet (see above). Van Beneden had asked in his will that his biography be written by Walter Flemming and Karl Rabl, published by them in a German periodical, and translated into French in Archives de biologie. Flemming was dead by 1910, so Rabl wrote the biography alone: “Edouard Van Beneden and der gegenwärtige Stand der Wichtigsten von ihm behandelten Probleme,” in Archiv für mikroskopische Anatomie, 88. (1915), 1–470, This extensive biography, in spite of all its good points, was considered by Van Beneden’s disciples as too polemic and too replete in allusions to Rabl’s own work, Its French translation was replaced, in the Archives de biologie, by a reproduction of Brachet’s notice.

Marcel Florkin