258 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



It was first discovered in 1922 in the changes of the gypsy moth, Lymantria, 

 from caterpillar to pupa to adult. Since then it has been shown in other in- 

 sects, among them moths, butterflies, and beetles. When the cerebral ganglia 

 of the brain were removed, the caterpillars failed to pupate even though they 

 were sufficiently mature. However, they did pupate when the ganglia were 

 removed from the head but transplanted into the abdomen. This implanting 

 was effective only if done a few days before pupation would otherwise have 

 begun. The secretions of minute glands, the corpora allata, closely associated 

 with the brain, also take part in the regulation of rates of growth, as in the 

 cockroach, and the changes of form such as from pupa to butterfly (Fig. 

 15.3). If these are removed from the early nymphal stage of a grasshopper, 

 the nymphal period is shortened, molts are suppressed and adult differentiation 

 begins prematurely. The hormone from the corpora allata, called the juvenile 

 hormone, causes insects to remain youthful. There are other hormones, pro- 

 duced by groups of neurosecretory cells in the brain, that stimulate molting 

 and pupation. It appears that some insects are capable of changing their form 

 at any time but are kept from doing so by the hormones circulating in their 

 blood. 



Vertebrates. Endocrine secretions are important to vertebrate animals 

 throughout their lives. They are effective not only in the animal in which they 

 develop, but in the bodies of animals into which they may be injected. They 

 may be taken from different species, even from different orders of animals. 

 Extracts of pig thyroid are commonly used for human thyroid deficiency. The 



ANTENNA 



BRAIN 



COMPOUND EYE- 



TRACHEAL TUBE 



ESOPHAGUS 



RECURRENT NERVE 

 CORPORA CARDIACA 



CORPORA ALLATA 





\ 



THORAX 



Fig. 15.3. A dissection of the head of a cockroach {Periplaneta americana) 

 showing the paired endocrine glands, corpora allata and corpora cardiaca. The 

 corpora allata secrete a hormone that prevents the insect from maturing pre- 

 cociously, i.e., before it has grown to its typical size. The glands can be removed 

 surgically after which the insect becomes a dwarf adult; if extra glands are grafted 

 mto an insect it becomes an immature giant. (Courtesy, Turner: General Endo- 

 crinology. Philadelphia, W. B. Saunders Co., 1948.) 



