38 SOURCES OF KINETIC AND METABOLIC HORMONES 



remain in their original paired positions and are innervated by the 

 pregangUonic fibres of the visceral motor or sympathetic system. 

 They secrete mainly noradrenaline. 



From Amphibia to Mammalia this tissue, having migrated 

 towards the anterior ends of the kidneys, becomes progressively 

 enveloped in the interrenal or cortical tissue, derived from 

 coelomic epithelium (§ 2.311). The chromaffin tissue forms the 

 adrenal medulla, or core, and secretes mostly adrenaline in 

 mammals. Together, the cortex and medulla form the complex 

 adrenal gland.* The cells of the medulla are innervated in. the 

 same way as in fish. Some unmodified ganglionic cells may be seen 

 among them ; but the chief characteristic of the tissue is the net- 

 work of blood spaces with which every cell is in contact and into 

 which their secretion can be passed with great rapidity in response 

 to nervous stimulation in an emergency (§ 3.11). 



2.12 ENDOCRINE GLANDS DERIVED FROM 

 ECTODERMAL EPITHELIUM 



A number of endocrine glands are derived from ectodermal 

 epithelium, without having any apparent connection with the 

 nervous system. These seem to be more frequent in invertebrates 

 than in vertebrates, and include the Y-organ and the prothoracic 

 glands, which are the main sources of the morphogenetic moulting 

 hormones of Arthropoda (§ 4.21 and Part II). The salivary 

 glands of Cephalopoda may be included here (§ 2.121), although 

 it is doubtful if their secretion is a true hormone. The corpora 

 allata of Insecta (§ 2.122) and the adenohypophysis of Vertebrata 

 (§ 2.123) are both important ectodermal sources of kinetic and 

 metabolic hormones. 



2.121 Salivary glands of Cephalopoda 



Salivary glands of cephalopods are primarily used for the 

 external secretion of tyramine, a poison for immobilizing the prey ; 



* Unfortunately, in medical terminology, this compound gland is 

 usually referred to as the "suprarenal", from its position "above" the 

 kidney in the upright posture. It must not be confused with the supra- 

 renal of fish, which is homologous with the medulla only. 



