624 TEXT-BOOK OF EMBRYOLOGY. 



to produce certain types of malformations. From this it was inferred 

 that the results of inhibiting the rate of development depend upon the 

 developmental moment at which the interruption occurred. These and other 

 results obtained by Stockard led him to the conclusion that changes in the 

 conditions of temperature and oxygen supply are the most frequent causes of 

 abnormal and monstrous development and embryonic death. In the 

 mammals, with their relatively constant temperature, the developmental 

 environment is under natural control, but it is not always perfectly regulated. 

 This lack of perfect regulation causes disturbances in the oxygen supply 

 which are regarded as potent factors in the production of malformations and 

 monsters. 



A significant fact relative to inhibition of development is found in the 

 normal production of quadruple offspring of the nine-banded armadillo. 

 In this animal the egg undergoes the early developmental stages up to 

 blastocyst formation while it is traversing the oviduct. When it reaches 

 the uterus the blastocyst lies in the lumen for about three weeks before 

 it becomes embedded in the uterine mucosa. During this period develop- 

 ment practically ceases, and the logical cause of the stoppage is the lack of 

 oxygen. Then when implantation occurs development sets in again and the 

 blastoderm divides into four embryonic rudiments which give rise to the four 

 offspring. 



As stated above, Mall attributed the production of monsters and malfor- 

 mations to faulty implantation of the ovum in the uterine mucosa with the 

 resulting disturbances in the nutritional relations of the developing embryo. 

 Stockard has added in this connection the specific factor of disturbance in the 

 oxygen supply. 



References for Further Study. 



AHLFELD, F.: Die Missbildungen des Menschen. Leipzig, 1880-1882. 



AHLFELD, F.: Lehrbuch der Geburtshilfe. Leipzig, 1903. 



BALLANTYNE, J. W.: Antenatal Pathology. 2 Vols. Edinburgh, 1904. 



BARDEEN, C. R.: Abnormal Development of Toad Ova Fertilized by Spermatozoa 

 exposed to the Roentgen Rays. Jour, of Exp. ZooL, Vol. IV, 1907. 



BEARD, J.: The Morphological Continuity of the Germ Cells in Raja batis. Anat. 

 Am., Bd. XVIII, 1900. 



CONKLIN, E. G.: The Cause of Inverse Symmetry. Anat. Aw., Bd. XXIII, 1903. 



DARESTE, C.: Recherches sur la production des monstrosites. Paris, 1891. 



DRIESCH, H.: Entwickelungsmechanische Studien. Zeitschr. f. wissensch. ZooL, Bd. 

 LIII, Bd. LV. 



FORSTER: Die Missbildungen des Menschen. Jena, 1865. 



GUDERNATSCH, J. F. : Hermaphroditismus vera in Man. Am, Jour, of Anat., Vol. XI, 

 1911. 



HERTWIG, O.: Urmund und Spina bifida. Arch. f. mik. Anat., Bd. XXXIX, 1892. 



