GENETIC TYPE AND THE ENDOCRINES 469 



of characters from the two parent stocks. The pituitary 

 glands in these F 2 type mixtures also present intermediate 

 and mixed histologic patterns, not clearly directed towards 

 either the extreme dachshund or the extreme Boston terrier 

 histology. Figures 5 and 6 in plate 89 illustrate longitudinal 

 sections through such pituitaries. Figure 5 is from F 2 294 2 , 

 shown photographed from life in plate 39, figure 2 (p. 236). 

 This bitch was killed as an adult of 2^ years; her bones 

 were heavy and well developed, and the skull was largely 

 dachshund in type, with strong muzzle, while the legs were 

 straight and long as in the Boston terrier. The pituitary 

 presents peculiarities quite commonly found in both stocks. 

 Boston terrier-like, the pars distalis does not fully encase 

 the nervosa and a large irregular cyst with columnar epithelial 

 lining extends through the anterior region of the pars distalis. 

 The pars intermedia is thick and irregular in outline, deeply 

 infiltrating the nervosa. On the other hand, the pars inter- 

 media evaginates far into the distal end of the nervosa, 

 with the space of the residual lumen following it; and the 

 chromophilic cellular types are abundantly and normally ex- 

 pressed, the acidophiles predominating about eleven to one; 

 all of these arc dachshund-like qualities. This gland no doubt 

 functioned quite normally. 



Figure 6 in plate 89 is from F 2 722 S , which had short legs 

 and a partly modified Boston terrier head. The pituitary is 

 short and thick with the general outline of the Boston terrier 

 gland, but is entirely free of cystic formations. 



In concluding this survey of the F 2 glands, we must repeat 

 that neither all dachshund nor all Boston terrier pituitaries 

 are of one definite pattern. The histology of this gland 

 varies among the individuals of each dog breed. Yet in spite 

 of this individual variability, the pituitaries from contrasted 

 breeds present histologic patterns which are quite consistently 

 different in detail. 



Further evidence on the genetic nature of such pituitary 

 patterns is furnished by the backcross hybrids from the 

 two parental stocks. 



