34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



caterpillar, which takes place in October, though pupation does not 

 occur until the following May. Also histological changes in the 

 Malpighian tubules begin just after the larva has spun its cocoon; 

 reconstruction of the tubules is completed in the pupa. After a short 

 rest the silk glands degenerate, and in the course of the winter a 

 part of the larval musculature is lost. 



Considering the growth of adult organs that may proceed in the 

 active larva, and the metamorphic changes that take place in the 

 quiescent larva after spinning its cocoon, it seems that there must be 

 some mechanism that regulates the hormone secretions. Actually, the 

 two hormone sources are in communication with the brain. The 

 thoracic glands receive their stimulus for activity from the hormonal 

 secretion of the brain by way of a pair of bodies in the back of the 

 head of nerve-tissue origin, known as the corpora cardiaca. These 

 bodies are directly connected by nerves with the secreting centers of 

 the brain, and a nerve from each corpus cardiacum goes to the corpus 

 allatum of the same side. It is possible, therefore, that the brain is 

 the regulatory center of the entire endocrine system. In fact, it has 

 been shown by Scharrer (1952) in the cockroach Leucophaea that 

 the corpora allata are affected histologically and functionally by the 

 amount of brain secretion in the corpora cardiaca. When the brain 

 nerve to one corpus cardiacum is cut, preventing the brain secretion 

 from entering the latter, the connected corpus allatum increases in 

 size, its cells appear to contain more cytoplasm, the nuclei become more 

 vesicular, and the nucleoli more distinct. Corpora allata in this condi- 

 tion, Scharrer says, are "functionally equal to, or perhaps even more 

 competent than, normally innervated glands." This would seem to 

 indicate that the more brain secretion there is in the corpora cardiaca 

 the less active are the corpora allata, and vice versa. The brain, of 

 course, does not act autocratically; it is itself activated by external 

 or internal stimuli transmitted through the sensory nerves. When the 

 brain activities cease, all growth and developmental processes stop, 

 and the insect goes into diapause. This is shown by Van der Kloot 

 ( 1955) to be true of the diapausing pupa of the Cecropia moth. After 

 prolonged exposure to low temperatures, endocrine activity of the 

 brain is restored, "diapause ends and the development of the adult 

 moth begins." 



Inasmuch as most animals grow from youth to maturity without 

 the aid of a juvenile hormone, it is not clear why or how the early 

 insects acquired glands for producing this hormone. However, it is 

 reported by Schneiderman and Gilbert (1959) that substances having 

 at least the effect of the corpus-allatum hormone when injected into 



