DECIDUOUS NATURE OF DEER ANTLERS 363 



doses of growth hormone were practicalh without effect on antler 

 growth, and Blauel ( 1935) observed tliat the growing antlers of the 

 roe deer were not influenced by administration of whole pituitary 

 powder. In recent experiments by the author, no effects were ob- 

 served on the autumn antlers of 2 sika deer injected with 1 gm of 

 lyophilized, defatted l^eef pituitary twice a week for 2 months. 



In view of these incomplete data, the course of research in the 

 future is inescapable. It is to approach the problem of antler shed- 

 ding in particular, and that of the recurrent annual cycle of antler 

 replacement in general, from a variety of directions. From the com- 

 parative point of view, valuable insight into the relationships be- 

 tween antler cycles and reproductive c\'cles may be gained by 

 seeking fuller knowledge of these phenomena in such aberrant forms 

 as reindeer and caribou, which have antlers in both sexes, and in 

 tropical species of deer, which often exhibit verv irregidar cvcles of 

 reproduction and antler succession. A sur\'ev of endocrine influences, 

 by extirpation experiments as well as hormone injections, may re- 

 veal how the various phases of the annual antler cycle are regulated. 

 Finally, it will be important to examine more closely the actual 

 mechanism of antler shedding. Since the earliest stages of a process 

 are so often the most important, by learning more about the de- 

 ciduous nature of antlers our understanding of their genesis and 

 growth may be enriched. 



Summary 



Antler shedding is accomplished l^v osteoclastic erosion of the 

 haversian lamellae along the line of demarcation between the dead 

 bone of the antler and the living bone of the pedicle. It is an integral 

 part of the sequence of histological events associated with the initia- 

 tion of renewed antler growth. 



In temperate regions, male deer lose their antlers in a fixed season 

 depending upon the species. This is determined by reactions to sea- 

 sonal changes in dav length, as has been proved by noting responses 

 to transequatorial shifts or exposure to experimentally altered day- 

 to-night ratios. Tropical deer show a tendency toward asynchronous, 

 and occasionally prolonged, antler replacement periodicities, to- 



