388 CHARLES Et. STOCKABD 



It is very difficult in dogs, as it would be in man, to demon- 

 strate that the genetic composition of the tissue determines 

 its pattern of growth without regard to the general state of 

 endocrine control. We felt that this problem would need 

 to be studied on a limited part capable of development along- 

 several different patterns, and that further advantage might 

 be gained were this part composed of a number of similar 

 segments. 



The deformities of the tail found in the bulldog breeds 

 arc particularly valuable for this investigation. These breeds 

 show localized chondrodystrophy deformities at both the 

 head and tail ends of the axial skeleton. In rare cases the 

 deformity may extend to intermediate parts of the vertebral 

 column, particularly the cervical and thoracic regions. This 

 is also true for the similar disturbance in man. The epiphyseal 

 cartilages in the tail vertebrae of the bulldog fetus are so 

 dystrophic that the entire tail is deformed into a corkscrew- 

 like twist, and shortened to a few centimeters in length. 



When the screw-tailed bulldog is crossed with the basset- 

 hound, which has a long, straight tail, all F x hybrids develop 

 perfectly formed long tails, as shown in plates 19 and 20 

 (pp. 97 and 99). The deformed tail is, therefore, recessive 

 to the normal. In the second hybrid generation, the tail 

 deformity reappears in several different patterns. The ma- 

 jority of the F L , animals have long, straight, freely jointed 

 tails; others have long tails that are permanently bent at 

 one or more places; a few have short, straight tails; still 

 others have short tails with a simple bend; and finally a 

 few, about one in sixteen, have the typical bulldog screw-tail. 

 This break-up in tail condition follows the typical genetic 

 behavior for a compound character consisting of two recessive 

 elements. Plate 19 (figs. 6-9) shows one litter of four F, 

 hybrids, and plate '20 (tigs. 5-8) shows the skeletons of these 

 animals. Three have long tails, and two of these long tails 

 are permanently bent (figs. 7 and 9, pi. 19; figs. 7 and 8, 

 pi. 20). Figure S in plate 19 presents the typical short twisted 



