442 SUMMARY OF CURRENT RESEARCHES RELATING TO 



glands are enlarged later, if they are enlarged at all. They appear to 

 increase in size with age (the length of life does not exceed two years), 

 while the sudorific glands attain their maximum at the breeding 

 season. 



Jobnsen has shown that there is a correlation between the ripening 

 of the testes and the growth of the sudorific glands of the lateral organ. 

 In quite mature males almost all the tubules are in secretory activity. 

 Thereafter a resting-period begins. In adult non-gravid females the 

 glands are in full secretion ; in gravid or lactating females (twice in 

 the summer) there is a diminution of the secretion or a regeneration 

 stage. The secretion appears to be repulsive to enemies ; but it seems 

 to be more directly connected with sex, facilitating recognition. 



Effect of Postponed Moult.* — C. W. Beebe gives a fresh descrip- 

 tion of his important experiments originally recorded in The American 

 Naturalist six years ago. The subjects of the experiments were males 

 of the Scarlet Tanager, Piranga erytkromelas Vielliot, and the Bobolink, 

 Dolichonyx oryzivoms (Linnaeus), in both of which a brilliant summer 

 plumage alternates with a totally different winter garb. The problem 

 of the research was " the discovery of the factors which determine this 

 seasonal change," but only one of the possible factors was investigated, 

 namely, " the condition of fatness or thinness of the bird's body, and 

 its influence on moult." 



Normally, the autumnal moult is associated with the thin and poor 

 condition that follows the stress and cares of the breeding season. In 

 these experiments tame tanagers and bobolinks which had not bred 

 were placed under careful observation at midsummer while " still in 

 the height of vocal and physical condition." The birds were kept in 

 small cages in a quiet room, and the light was gradually cut down, 

 while the food supply was slightly augmented. Under these conditions 

 they became very quiet and inactive, and rapidly put on fat and in- 

 creased in weight. These conditions were maintained without ill effects 

 on the subjects, but with the important result that the autumn moult- 

 ing time passed without a single feather being shed. Mid-winter thus 

 found the birds in their summer dress, and it was noted that if one 

 was temporarily brought into a stronger light, and had meal worms 

 added to its diet, the song was fully resumed for a limited period. A 

 sudden alteration in temperature, whether upwards or downwards, brought 

 about a diminution in weight ; one tanager that lost weight rapidly under 

 such circumstances underwent a belated moult into the green winter 

 plumage. 



" Early in the following spring individual tanagers and bobolinks 

 were gradually brought under normal conditions and into their seasonal 

 activities, with quick result." The spring moult took place, and the 

 birds went directly from one nuptial plumage to another. " The old 

 scarlet and black feathers fell from the tanagers, and were replaced by 

 others of the same colour ; and from buff, cream, and black, the bobo- 

 links moulted into buff, cream, and black !" In every case the inter- 

 vening winter plumage had been entirely suppressed. 



* Zoologica, i. (1914) pp. 253-8. 



