494 CHARLES R. STOCKARD AND E. M. VICARI 



normal, low-functioning thyroid. Figure 2 shows a histologic 

 section of the thyroid from a heavily typed male English 

 bulldog, 120 $ . The follicles are very small and contain little 

 or no colloid, and the epithelium is high columnar. Much 

 interfollicular tissue is present, and there are pathologic 

 conditions in the gland other than simple hyperactivity. The 

 histologic pictures of the bassethound and bulldog thyroids 

 could scarcely be more completely contrasted. 



The F! bassethound-bulldog hybrids show a thyroid histo- 

 logic pattern which is quite consistent and differs from both 

 parental stocks. These thyroids contain large and small fol- 

 licles, many being as large as those of the hound and others 

 as small as in the bulldog, although somewhat more regular 

 in outline. The follicular epithelium in all these glands is 

 high columnar and is more active than in the bassethound. 

 Figures 3 and 4 (pi. 93) illustrate the histology of the thyroids 

 from two Fj brothers, 739 $ and 741 $ , both of which were 

 3 years old when killed. The physical types of the parents 

 and the Fj animals are illustrated from life in plate 19 (p. 97). 



Figures 5 and 6 illustrate the histological qualities of 

 thyroids from two very dissimilar F 2 hybrid brothers, 1313 $ 

 and 13125. These dogs were not quite 2 years old when 

 killed. No. 1313 $ weighed 20 kilograms and was of about 

 the usual size for such hybrids. The brother, 1312 $ , was 

 much larger and weighed 30 kilograms. These two animals 

 are shown in front and side views in plate 22 (p. 102). No. 

 1313 $ has the size, shape and general appearance of the 

 bassethound grandparent, while 1312 $ resembles neither the 

 bassethound, as does 13135 (figs. 3 and 6), nor the bulldog, 

 as does 1311 $ (figs. 1 and 4). His head, face and general 

 bodily appearance and proportions are of the mastiff and 

 the short haired St. Bernard type. This animal possessed a 

 large and solid thymus body, while both the bassethound- 

 like and bulldog-like brothers had only a small amount of 

 loosely scattered thymic tissue. 



Figure 5 in plate 93 shows a section of the thyroid from 

 the bassethound-like F 2 hybrid. The epithelial pattern of 



