398 V. THE NATURE OF EVOLUTION 



syndrome which they elicit. Their influence upon the cortex is me- 

 diated by the anterior lobe of hypophysis and prevented by hypophy- 

 sectomy. 



It is considered that the effect of such damaging agents or the 

 stress is first received by the anterior lobe of hypophysis with the 

 increased secretion of adrenocorticotrophic hormone which induces the 

 adrenal cortex to produce corticoid-hormone ; the production of gonad- 

 trophin and thyrotrophin, on the contrary, may be diminished by the 

 same stress. 



Of the various environmental factors, climatic ones seem to be 

 most closely connected with animal and vegetable life, whereas it is 

 supposed that also the climatic effects are received mainly by hypo- 

 physis or pituitary gland, and that seasonal cycles of pituitary activity 

 that are reflected by cytologic change or bioassay are known to occur 

 throughout animals especially in vertebrates. It is reported that a 

 combination of environmental factors, including amount of rainfall, 

 mean temperature, and a food supply, affects the pituitary cycle of 

 some animals (75). Moreover, it is stated that the breeding season 

 rhythm of all amphibia is under the anterior pituitary control, which 

 is in turn influenced by nervous factors, and the final release of pitui- 

 tary hormones is thought to occur in response to complex climatic 

 changes. Internal sexual rhythms are usually adjusted to externa' 

 seasonal change. 



It is generally acknowledged that water metabolism of man is 

 extensively effected by climatic factors, wheras it is known that the 

 water metabolism is subjected to the function of adrenocorticotrophic 

 hormone of hypophysis. On the other hand, the features of plant 

 activities such as flowering and fruit bearing are, as is well known, 

 governed by climatic factors, such as temperature and light, whilst it 

 is believed that in this connection hormones or related substances play 

 an important part. Some animals such as the chameleon can promptly 

 change the colour-pattern in response to the colour of back ground. 

 Such a colour change in several vertebrate species depends upon 

 stimulation of the eyes which is transmitted to the endocrine glands, 

 which in turn produce hormones acting directly upon the pigment 

 cells, chromatophores. 



The interfering action of hormones upon genes is remarkable as 

 already emphasized, and consequently changes in the feature of 

 hormone secretion induced by environmental factors may be able to 

 have influences peculiar to the changed feature upon the genes of 

 germ cells leading to the formation of peculiar characters of the orga- 

 nisms. However, the effect of hormones cannot be so specific as can 

 produce the amazingly specific adaptation of organisms. The specific 



