368 H. H. Newman and J. T. Patterson. 



embryo vesicle. In another case (no. 17), which is peculiar in 

 several other respects, there occurred a small empty amniotic 

 sac fused firmly to the wall of the Trager and connected with 

 the amniotic sac of a normal embryo by means of an amniotic 

 canal similar to those of the other embryos. In still another 

 case (no. 9) a fairly large sac in the Trager region was connected 

 by means of a poi'fect amniotic canal with that of a normal 

 embryo (fig. 44) . There is little doubt but that these sacs repre- 

 sent the remnants of supernumerary embryos and as such are 

 the equivalent of those described by von Jhering and Fernandez. 

 It is interesting to note in this connection that Tatu novem- 

 cinctum shows a stronger tendency toward stability in the number 

 of foetuses in a litter than does T. hybridum. There is evident, 

 however, in the latter species, a tendency to produce eight young 

 in a litter, just twice the number typical for our species. The 

 numbers of individuals in a litter ranges, however, from seven to 

 twelve. 



B. Arrangement of Embryos 



In order to clear the way for the description of the early embry- 

 onic conditions it should provisionally be pointed out that the 

 four embryos of this species are arranged in pairs, one pair to 

 each lateral half of the uterus. The upper embryo of the left 

 hand pair usually occupies the dorsal amniotic quadrant and is 

 therefore referred to as the ''dorsal embryo " (no. Ill) . The lower 

 embryo of the left hand side occupies the left lateral amniotic 

 quadrant and is referred to as the ''left lateral" embryo (no. 

 IV). The lower embryo of the right hand pair occupies the ven- 

 tral amniotic quadrant and is the "ventral embryo" (no. I), 

 while its mate, occupying the right lateral quadrant is spoken of 

 as the "right lateral" embryo (no. II). Nos. I and II constitute 

 the right hand pair and nos. Ill and IV the left. 



The orientation of the vesicle in the uterus and the arrange- 

 ment of the four embryos with reference to the vesicle and to 

 one another is rather precise, so that a plane running from the 

 mid-dorsal to the mid-ventral line of the uterus would divide 



