George B. Wislocki 641 



Marshall concludes, however, that ruminants, including deer, are excep- 

 tional, since, if they react to light at all, it must be to diminution rather than 

 to increase, because their breeding season, both north and south of the equator, 

 falls in the period of diminishing daylight. If one be permitted to carry this 

 interesting analysis and spectdation somewhat further, what apparently puz- 

 zles Marshall about the ruminants can perhaps be harmonized to some extent 

 with the behavior of other mammals. MarshalP"'^ does not consider the pe- 

 riodicity of the antlers of deer, but it is clear from the observations of Donne^^ 

 that, in the transference of deer across the equator, not only does the breeding 

 season shift but the whole antler-gonadal cycle is also shifted to accord with 

 the new climatic or seasonal environment. 



If we consider now the antler-gonadal seqtxence as related phenomena 

 and as a whole, it appears jtistifiable to assume from the sequence observed 

 in Virginia deer that the initiation of antler growth and the activation of the 

 gonads occur in succession in the climatic spring or early summer. And if we 

 assume on the basis of the accumiulated evidence that seasonal periodicity is 

 related to exteroceptive stimuli, we may postulate with some validity from 

 examination of various species of deer that the seasonal growth of the antlers 

 and of the gonads is initiated sometime in the spring or early summer by the 

 influence of light acting through the hypophysis.* Furthermore, it seems rea- 

 sonable to assume froin the data on the growth of antlers and testes that the 

 hypophysis first releases an antler-stimulating hormone which is followed one 

 to two months later by the release of gonadotrophic hormones. The former 

 stimulates periosteal hypertrophy in the antler pedicles and initiates the proc- 

 ess of ossification. The latter activate the interstitial tissue of the testes and 

 initiate spermatogenesis. The androgenic hormones, so stimulated in the 

 testes, in turn subsequently influence and regulate the full maturation of 

 the antlers. Finally, the casting off of the antlers occurs when the testes are 

 declining, but is precipitated immediately if castration is resorted to in the 

 fall; consequently dropping of the antlers must be due to a decline or removal 

 of gonadal hormone. 



Regarding the relationship of initiation of antler growth to activation of 

 the testes, it is apparent that in the European roe deerj- a similar situation 

 prevails to that here observed in the Virginia deer. From perusal of data for 

 this deer one finds that the antlers make their appearance from December to 

 February (Brehm'°), whereas, according to Stieve,^" spermatogenesis does not 

 commence until April. Thus it seems justifiable to conclude that, as in the 



* The pituitaries of the present series of deer have not been studied histologically. The 

 adrenals, however, have been examined histologically by Dr. H. Stanley Bennett of this de- 

 partment. He reports that no apparent seasonal variations are present in the specimens with 

 regard to cortical zoning or staining of the cells, as revealed by Masson's technique. The 

 thyroids of the same deer have also been the subject of study by Dr. A. L. Grafflin."^ uho re- 

 ports that he has been unable to demonstrate seasonal variations in the material from that 

 gland. 



f See footnote on page 635. 



