II. SIZE OF THE BODY AND OBGANs 



91 



parathyroid glands. Her dissection records show the rela- 

 tions given in table 21. 



It appears that in the generations of captive Grays from 

 G L , to G 10 the thyroid was missing on one side in twelve cases 

 and defective in two others. The total number of rats exam- 

 ined was 449. In five cases the corresponding parathyroid 

 was also missing. In thirteen out of fourteen cases the defect 

 was on the right side, and twelve of the fourteen rats were 

 females. Here is a series of defects, in the thyroid and para- 

 thyroid, which occur predominately in females and on the 

 right side. The parathyroid is missing in less than half the 

 cases. Four of these five cases of missing parathyroid were 

 in G 10 . 



The skulls which were prepared from this generation 

 showed several instances of defective incisors a condition 

 probably related to deficiency in parathyroid secretion (Ham- 

 mett, '22). It may be said, further, that these structural de- 

 fects seem, so far, to be a peculiarity of this series of captive 

 Grays and have been noted heretofore only in one instance, 

 a hybrid Norway X Albino out of hundreds of rats dis- 

 sected. 



TABLE 21 



Record of deficiencies in the thyroid and parathyroid gland*. Captive Gray* 



fourteen cases 



