HORMONES 



65 



of what are comparable with endocrine organs. Facts are being 

 brought to hght which lead to the conclusion that ecdysis, meta- 

 morphosis, and also the full maturing of the gonads, are controlled 

 through the intervention of certain secretions. Since the evidence 

 all points to the fact that these secretions are discharged into the 

 blood, they are therefore comparable with hormones of the 

 endocrine type. As in Vertebrata, they appear to be produced 

 by ductless glands and have a very definite effect upon other 

 organs and tissues. In insects, a pair of small bodies, known as 



Fig. 35. Dorsal view of brain and associated parts of a winged 

 Termite, al, antennary lobe ; ca, corpus allatum (left) ; fg, 

 frontal ganglion ; o, oesophagus ; ol, optic lobe ; pn, posterior 

 sympathetic nerve (left) ; rn, recurrent nerve ; sg, oesophageal 

 sympathetic ganglion (right). Original. 



the corpora allata (Fig. 35), found in association with the sym- 

 pathetic nervous system, a short distance behind the brain, are 

 almost certainly endocrine organs. The corpora allata arise in 

 the embryo as ectodermal invaginations, usually of the mandibular 

 segment. Subsequently they lose all connection with the exterior 

 and finally assume the form of small, ovoid, whitish bodies which 

 were formerly mistaken for a pair of posterior sympathetic 

 ganglia. Histologically, they differ from nervous tissue and have 

 rather the features of glandular organs. They occur in all orders 

 of insects and their structure was studied in considerable detail 



R.A. ENTOMOLOGY. 3 



