HEREDITY AND ORGANIC SYMMETRY IN ARMADILLO. 3 



Before the reader can appreciate the significance of the data 

 on heredity and organic symmetry, it will be necessary for him 

 to be made familiar with the character of the material and its 

 specific frequency and distribution. 



MATERIAL AND METHODS OF STUDY AND PRESENTATION. 



The material for this investigation consists of nearly two 

 hundred sets of quadruplet fetuses in advanced stages, showing 

 the definitive arrangement and number of scutes in the armor. 

 In every case the shell of the mother was obtained and preserved 

 so that there is on hand complete data on uniparental inheritance 

 of armor characters. The fetuses and the respective mothers 

 make up a collection of nearly one thousand individuals, which, 

 is unquestionably a representative sample of the species. 



Counts of scutes and records of anomalies have been made- 

 independently by at least two workers and all differences or dis- 

 crepancies have thus been checked and corrected, so that the 

 probability of error and personal bias have been eliminated. 



Since the anomalies here dealt with are rare, occurring in 

 only about three per cent, of individuals, I have made an examina- 

 tion of the preserved armor of 1,800 adults that formed the stock 

 of a single dealer. This was done in order to determine the 

 limits of diversity and the specific distribution of the anomalies., 

 A complete record of all these anomalies has been made in the 

 form of a pictorial diagram in Table A, I, 2 and 3. 



In order that the reader may understand the nature of the 

 anomalies it will be necessary to give a brief statement of the 

 normal relations of armor units. The primary unit of the armor 

 is a threefold complex consisting of a bony plate, covered by a 

 primary epidermal scale of scute, and a group of hairs that are 

 imbedded in the bony plate and perforate the scute. For con- 

 venience this complex is called a "scute." In young fetuses the 

 outline of the epidermal scute is all that can be seen ; but this 

 visible unit stands for the whole complex. These scutes or 

 armor units of the carapace are arranged differently in the three 

 main subdivisions of the armor, the pectoral, banded and pelvic 

 shields. In the pectoral and pelvic regions the bony plates are 

 arranged like tiles and form a rigid immovable shield. Naturally 



