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Nachdruck verboten. 



A Preliminary Report on tiie Demonstration of Polyembryonie 

 Development in the Armadillo (Tatu novemcinctum). 



J. Thomas Patterson, university of Texas. 

 (Contribution from the Zoological Laboratory, University of Texas. No. 110.) 



With 10 Figures. 



It has been shown that the North American species of the arma- 

 dillo gives birth to four young at a time, and that the individuals of 

 a given litter are always of the same sex. Furthermore, the four 

 embryos are enclosed Avithin the same chorionic vesicle. These facts 

 have called forth the conclusion that the development of this animal 

 is a form of polyembryony. 



So far no one has succeeded in demonstrating the validity of 

 this conclusion, although work done on rather late embryonic 

 development has revealed a line of evidence supporting the idea of 

 polyembryony^). But conclusive evidence can only be claimed after 

 one has had the opportunity to study a complete series of early stages, 

 especially those that show exactly the origin of the four embryos. 



It has recently been my good fortune to have secured about 

 fifty early stages, more than half of which are younger than any 

 that have been heretofore described; and these stages represent 

 practically an unbroken series through the period of embryo formation. 



We shall begin the account with the description of a vesicle 

 about to pass from the fallopian tube into the uterus. At this time 

 the vesicle measures about .265 mm in diameter, and consists of 

 a trophoblastic layer of polygonal cells arranged in mosaic and of an 

 inner cell mass located at the animal pole of the vesicle. It can 

 easily be made out from sections that the inner cell mass has not 

 differentiated into its two primary components, the hypoblast and 

 epiblast (Fig. 1). There are, however, two distinct types of cells. 

 The bulk of the mass consists of rather large, ill-defined cells, the 



1) Newman and Patterson, Journal of Morphologj" Vol. 21, No. 3; also 

 Fernandez, Morphologisches Jahrbuch, Bd. 39, Heft 2. 



Anat. Aiiz. Bd. 41. Aufsätze. ^^ 



