A PROBABLE EXPLANATION OF POLYEMBRYONY IN 

 THE ARMADILLO 



PROFESSOR CHARLES R. STOCKARD 

 Cornell University Medical College, New York City 



By arresting the development of the fish's egg during early 

 stages double individuals and twins are frequently induced. 

 The interruption or arrest makes it possible for more than one 

 potential growth point along the germ-ring to give rise to an 

 embryonic shield. In other words, accessory invaginations or 

 blastopore formations occur as the initial structural step in 

 doubleness. The interruption in the development of the fish 

 embryo must be introduced during the cleavage stages and be- 

 fore gastrulation in order to produce such phenomena. Among 

 hundreds of eggs arrested during later developmental stages no 

 double monsters or twins ever occurred. A complete account of 

 these experiments is soon to be published but for our present 

 purpose two facts are important : First, accessory embryo forma- 

 tions result from arrests in the developmental process; and 

 second, the arrest must occur before gastrulation has taken 

 place. 



In the light of these experiments it has seemed possible to 

 interpret somewhat more clearly than has formerly been done 

 the remarkable phenomenon of multiple embryo formation in 

 the armadillo. 



On examining the uterus in two pregnant specimens of a 

 South American armadillo von Jhering, in 1885, discovered that 

 each contained eight fetuses enclosed within a single chorion. 

 He correctly concluded that all of the fetuses in each mother 

 had been derived from a single egg by some process of division 

 into separate embryonic rudiments. After this valuable dis- 

 covery and interpretation, the study of the armadillo's develop- 

 ment lapsed and nothing of importance was added for almost 

 twenty-five years. Two series of investigations were then be- 

 gun sinmltaneously one on the Texas armadillo by Newman and 

 Patterson/ and the other on the South American species by Fer- 



1 H. H. Newman and J. T. Patterson, Jour. Morph., Vol. 21, p. 359, 1910. 

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