Bauhaus-Universität Weimar

The Development of the Nine-banded Armadillo from the Primitive Streak Stage To Birth; With Especial Reference to the Question of Specific Polyembryony
Newman, H. H. Patterson
Development of the Nine-Banded Armadillo. 399 
On the whole however, in spite of these exceptions, the general 
rule holds good, that the closest resemblances occurs between 
paired embryos. 
In this connection it should be mentioned that even where 
there is exact resemblance between the individuals of a pair in 
the total number of scutes in the nine bands of armor, there is 
no perfect correspondence with respect to individual rows. The 
resemblance in total numbers of scutes is however, a matter of 
more importance than the exact manner of their arrangement 
into rows, which is a secondary process. Each primary scute 
is the equivalent of a well defined hair group and these groups, 
as can be seen in other regions of the body, are quite definite units, 
although subject to more or less shifting before reaching their 
final arrangement into rows. In a subsequent paper we expect to 
make a special study of variation and heredity in the elements 
of the armor and shall in this place refrain from any more detailed 
reference to the subject. 
Another source of data, however, which furnishes striking evi¬ 
dence of pairing is seen in connection with a fairly common ten¬ 
dency for regional fusion of adjacent bands of armor, or for the 
occurrence of interrupted and of incomplete bands in definite 
regions. Such atypical conditions occur in from three to four 
per cent of all cases, a fact that we have established from an exam¬ 
ination of considerably over a thousand shells. This comparative 
rarity of occurrence, while it renders the collection of data on 
pairing and identity difficult, gives to such data an added value, 
in that chance resemblances are very unlikely to occur. 
Only four cases of strikingly atypical armor arrangements have 
so far been discovered in the collection of foetuses now in our 
possession. In one case in embryos I and II there occurred a 
remarkably atypical scute arrangement in the first band of 
armor, while III and IV were quite normal. In a second case 
I and II showed a slight fusion between the first two rows at the 
right hand margin, while III and IV showed a much more exten¬ 
sive fusion in exactly the same region. The pairing in this case 
was only a matter of degreeof fusion, but there was a decided differ¬ 
ence in extent of the region of fusion in the two pairs. In a third


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