GENETIC TYPE AXD THE EXDOCEIXES 473 



connection is the fact that the pituitaries from backcross 

 Boston terrier hybrids are closely Boston terrier in pattern, 

 and likewise that the backcross hybrid is an approach to the 

 Boston terrier in type. In its complete detail, the thyroid 

 of this backcross hybrid 524 $ , is of the extreme Boston 

 terrier pattern, as is well seen in figure 3 of plate 86. This 

 thyroid is very different from the F x gland (fig. 3, pi. 85), 

 and would seem to be more completely Boston terrier than is 

 the pituitary, but this may be due to its much simpler 

 microscopic pattern. 



Again, figure 2 (pi. 90), from backcross Boston terrier 

 525 $ , could very well pass as a defective Boston terrier 

 pituitary. In this specimen the cord-like arrangement of the 

 cells in the pars distalis, along with a high proportion of 

 basophiles, resembles more closely certain of the pure Boston 

 terrier glands than any of those from the ¥ A hybrids. The 

 thyroid in this animal is also of perfect Boston terrier quality 

 (fig. 4, pi. 86). 



Figures 3 and 4 in plate 90 are decidedly different from 

 figures 1 and 2, both in general appearance and in detail, 

 and these differences are comparable to those cited as dis- 

 tinguishing the pituitary of the Boston terrier from that of 

 the dachshund. In figures 3 and 4, the pars distalis is long, 

 and encases the pars nervosa in a manner similar to that 

 common for the dachshund gland. In many of the backcross 

 dachshund pituitaries no cysts are present, but in each of 

 these two sections we find a single small cyst with the low 

 inactive or degenerate epithelial lining occasionally found in 

 the dachshund gland. These cysts are very unlike those of 

 the Boston terrier and F x pituitaries. Figure 3 represents the 

 pituitary from 349 $ backcross dachshund, which is shown from 

 life in plate 45 (p. 248) and is seen to be almost exactly dachs- 

 hund in character. Figure 4 (pi. 90) is from a sister, 343 9 , 

 who is also shown in plate 45. Both these sections of pitui- 



