Paper - A study of the causes underlying the origin of human monsters 2

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Mall FP. A study of the causes underlying the origin of human monsters. (1908) J Morphol. 19: 3-368.

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A Study Of The Causes Underlying The Origin Of Human Monsters

Recent Work Upon the Production of Polysomatous Monsters

The various theories regarding teratogenesis which had troubled mankind for so many centuries were finally exploded by naturalists, whose speculations gradually led them to experiment upon this subject. Anatomists and zoologists had deduced that the primary change lay in the egg about the time of fertilization, and we read in J. Muller,’ Valentin’ and Leuckart3 that a double monster is due to division of the embryo—forming substance in the earliest stage of development. The experiments subsequently made by Gerlachf Panum‘ and Dareste° upon chicks were negative in this respect, but the tradition has come down to us that polysomatous monsters are produced by a process of splitting of the primitive streak. The more recent anatomists—Fol, Rauber,

‘Muller, Meckel’s Archiv, I828.

‘Valentin, Handwiirterbuch d. Physiologic, I, 1842.

‘Leuckart, De Monstris, Giittingen, I845.

‘Gerlach, Doppeln-iissbildungen, I882.

‘Panum, Entstehung der Missbildungen, 1860.

‘Dareste, Recherches sur la production dc monstrosités, Paris, 1891.. 18 MALL. [VoL. XIX.

Born and O. Hertwig—who observed the developing egg and experimented upon it, were at first inclined to the theory that the first cause in the production of monsters is due to polyspermy, but this has not been substantiated.

The first reliable and valuable observations upon the production of double monsters were made by Veidovsky who noticed that the eggs of Lumbricus produce more monsters in warm than in cool weather, and he expressed the suspicion that they were produced by the change in temperature. Driesch seized upon this idea, experimented upon sea-urchins’ eggs, and found by subjecting them to high temperatures that the cells, in the two—cell stage, separated, each growing into an individual, but, however, remaining connected with each other. Driesch had already shown that when the blastomeres of these eggs are fully separated by shaking, each grows into a whole embryo, and it was now clear to him that double monsters are produced by separating the blastomeres slightly, but still keeping them close enough together so that the independent embryos grow into each other’s bodies to form a double individual.

By a very different method double monsters were also produced by Loeb. He subjected sea—urchin eggs to an equal mixture of sea-water and distilled water shortly after they had been fertilized. The rapid absorption of water caused many of the cell membranes to burst, and part of their protoplasm escaped, which, however, remained connected with that inside of the membrane. All this took place before the nucleus had divided. Upon returning the eggs to normal sea-water cleavage began, and one of the first two nuclei wandered into the extruded protoplasm. Each nucleus with its protoplasm then became an embryo, and in case the embryo within the egg was not separated from the extra-ovate embryo by its active movements in the blastula and gastrula stage a double monster or “Siamese” twins were formed. Frequently they became separated and independent animals developed. It often happened that the outflow of protoplasm was multiple, and then the three, or even more, protoplasmic drops which were formed developed respectively into triple or quadruple monsters.

These important discoveries were soon extended to the vertebrates by E. B. Wilson, who experimented upon the eggs of Amphioxus, and by O. Schultze, who experimented upon those of the frog. Wilson partly separated the blastomeres of Amphionus in the two-celled stage and produced a variety of double monsters which developed until the first gill-slits were formed. In the gastrula stage almost every possible transition occurred between forms slightly expanded laterally to those in which the two bodies were joined only by a slender bridge of tissue. Incomplete separation of the blastomeres in the four-celled stage gave rise sometimes to double embryos of equal size, triple embryos, one being as large as the other two, or rarely to quadruple monsters. Wilson’s studies prove, he believes, “that the unity of the normal embryo is not caused by a mere juxtaposition of the cells, but they indicate that this unity is not mechanical but physiological, and point toward the conclusion that there must be a structural continuity from cell to cell that is a medium of coordination, and that is broken by the mechanical displacement of the blastomeres.”

Oskar Schultze produced monsters in frogs by fixing the eggs between two glass plates, and after they had developed to the morula stage the plates were inverted. A number of the eggs righted themselves, but others grew into double embryos. Wetzel extended the observations of Schultze and showed that there was a flow of protoplasm in each of the blastomeres into their upper hemispheres, which may account for the separation of the primary cells, thus laying the foundation for two embryos instead of one.

Spemann has also produced polysomatous monsters from the frog’s egg by tying a ligature loosely around it in the twocell stage between the two blastomeres. Specimens in which the ligature struck the median plane of the embryo produced two-headed monsters of all grades, their development depending somewhat upon the degree of the mechanical constriction. He performed similar experiments upon Triton eggs, and in some instances found cyclopia in one or both of the heads. By broadening the anlage of the tail through splitting, a double tail may be formed, or in case limb-buds are divided one or more times two or even a cluster of limbs may be produced where but one develops normally.“

The experiments enumerated above, although not quite to the point in the present study, are reviewed because they show that teratogenetic problems are solved by experimental embryology and because they are very striking. If it is clear that polysomatous monsters are produced experimentally with such precision, the great variety of merosomatous terata of the experimenter must be admitted worthy of careful study. It is necessary to state this because only a small per cent of them live for some length of time, but they show a great similarity with early stages of human terata with which we are familiar. A glance at the great works of Dareste and Panum makes it clear that the deformed embryos they obtained are not easily interpreted and they could easily be pushed aside as not bearing upon the subject in question. The same criticism may be made against early pathological human embryos. That it is difficult to see any marked relation between them and monsters at the end of pregnancy caused me much confusion for a long time, but after studying a large number of deformed embryos I am finally convinced that the pathological embryos are nothing but young monsters. This conclusion is supported especially by the numerous investigations in experimental embryology, many of which are also at the same time investigations in experimental teratology. For this reason I shall consider briefly the recent work upon the production of merosomatous monsters.

“Tornier, Roux’s Archiv, XX, I905.