40 SOURCES OF KINETIC AND METABOLIC HORMONES 



become polyploid by division of their nuclei without cell division. 

 They form giant cells (g.s.c, Fig. 2-9). When secretion is com- 

 pleted, the gland returns to the initial undifferentiated state shortly 

 before the actual moult (Mendes, 1948). The glands also secrete 

 metabolic (§5.11) and morphogenetic hormones (Part II, §3) 

 during the adult life of the insect, v^hen the histology of secretion 

 appears to be the same as that in younger stages, and gives no 

 indication of the hormones being different at different ages. 



2.123 Adenohypophysis of Vertehrata 



The adenohypophysis, or the anterior lobe of the pituitary body, 

 is the only endocrine gland which arises from non-nervous ecto- 

 derm in vertebrates. Its origin is the hypophysis, an upgrowth 

 from the roof of the stomodaeum. It meets the brain and induces a 

 downgrowth from the hypothalamus or floor of the diencephalon ; 

 together they form the pituitary body (Fig. 2-13). Throughout 

 the vertebrates the contribution from the nervous system forms 

 the neurohypophysis which has already been described (§ 2.114). 



The subdivisions of the ectodermal adenohypophysis are 

 difficult to homologize in different groups. It has recently been 

 recommended (Pickford and Atz, 1957) that the noncommittal 

 terms pro-, meso- and meta-adenohypophysis should be used for 

 fish and that these should only be very tentatively homologized 

 with the three parts recognizable in most tetrapods, namely the 

 PARS tuberalis, the pars distalis and the pars intermedia (Fig. 

 2-10).* Of these, the pars distalis is usually the largest and appears 

 to be the main source of hormones. It lies in front of the original 

 hypophysial cavity, or cleft, if this persists, whereas the pars 

 intermedia forms behind the cleft and often comes into close 

 contact with the adjacent neural lobe. The pars tuberalis surrounds 

 the infundibular stalk. The shapes and relative sizes of these parts 



* Unfortunately, the old nomenclature is still to be found in many 

 books; in this, the pars intermedia, although formed from the same tissue 

 as the rest of the adenohypophysis or "anterior lobe of the pituitary", is 

 included with the pars nervosa in the so-called "posterior lobe of the 

 pituitary"; this is due to its morphological position in some mammals. 

 Other writers use posterior lobe as synonymous with the neural lobe, or 

 pars nervosa, only (Fig. 2-10). The names used here follow those recom- 

 mended by the International Congress of Anatomists (Woerdeman, 1957). 



