DEPARTMENT OF GENETICS. 



105 



doves. Essentially similar curves have been obtained for two additional 

 groups of birds. Though only one of the expected effects of suprarenal 

 hypertrophy has been investigated, the result clearly indicates that "the 

 enforcement in pigeons of frequent and continuous ovulations throughout the 

 year, as this has been practiced and reported by Whitman and by Riddle, 

 with important results on sex, viability, and longevity of offspring, is doubtless 

 accompanied by an increased and nearly continuous mobilization of carbo- 

 hydrate in the female parents." 



A study of the effects of some of the products of the endocrine glands 

 upon the storage metabolism of ova has yielded some definite results which 

 clarify and confirm Dr. Riddle's earlier interpretation of this matter. Among 

 these glandular products are some which are well known to have marked 

 effects upon the basal metabolism of the organism. Of these glands the 

 thyroid has the most pronounced effect in increasing the metabolism. Dr. 

 Riddle has demonstrated that the oral administration of thyroid, in quantities 

 so small as to be compatible with continued reproduction by normal healthy 

 females, distinctly diminishes the storage metabolism of the ova being pro- 

 duced. It would seem necessary to conclude that this reduced storage 

 (smaller yolk size) is a reflection of the increased oxidation which is known 

 to characterize the action of this substance on the body as a whole. From 



Table 1. — Effects of desiccated thyroid {20 mg. daily) on the storage metabolism of the ova 

 {yolk weight) of a single ring-dove during one year; 6 control eggs alternating with 6 

 treated eggs. 



the beginning of Dr. Riddle's studies in 1911 he has been led by other kinds 

 of evidence to interpret high storage values of the yolk to mean low oxidizing 

 capacity. Still further confirmation of this interpretation has been obtained 

 from similar studies with the products of other glands of internal secretion. 

 The whole of these data will be summarized at an early date and form a 

 chapter of a volume now in preparation. A summary of the data obtained 

 during one year from a single thyroid-fed female is given in table 1. 



Dr. Riddle earlier reported that one unique bit of evidence for the correla- 

 tion of large yolk-size of the egg with femaleness in the embryo which arises 

 from it has been obtained from measurements of twin-producing eggs. The 

 important fact was that all of the few female single-yolk twins obtained in 

 this research were associated with yolks demonstrably of extremely large 

 size. On the basis of his illuminating experiments on twinning and double 

 monsters in fish embryos, Stockard has recently suggested that twins in birds 

 probably arise in those particular eggs which are laid prematurely. If such 

 eggs are laid a few hours earlier than is normal, the process of gastrulation in 

 the embryo would have to occur at the prevailing lower temperature of the 

 air. On Stockard's view a lowering of the temperature during the sensitive 

 period of gastrulation induces double gastrulation and resultant twins. 



