§ 2.113 SECRETORY CELLS FROM THE NERVOUS SYSTEM 31 



hormone (§ 3.221) and of the metabolic diapause hormone (§ 5.112). 

 In the cockroach, Leiicophaea, these cells present a variety of 

 appearances in fixed preparations (Fig. 2-2). These probably 

 represent phases in secretion ; but this has not been confirmed in 

 the living animal. 



Neurosecretory cells of the brain 



Paired groups of neurosecretory cells are to be found in the 

 brains of insects, as in crustaceans ; but in most insects they appear 

 to be confined to the protocerebrum and not to extend into other 

 parts of the brain or optic lobes. The neurosecretory cells usually 

 lie in groups: the median neurosecretory cells (m.n.c, Fig. 2-3) 

 lie anteriorly near the mid-line and other cells lie ventrally or 

 laterally (l.n.c). The former are connected to the corpus cardi- 

 acum of the opposite side by an internal nerve, and the latter by 

 an external nerve (Fig. 2-8). Their axons lead into the corpora 

 cardiaca, where their secretion is stored (Fig. 2-9). The lateral 

 neurosecretory cells may represent the frontal organs of Aptery- 

 gota and may even be homologous with the cells of Planstrom's 

 sensory pore organ (§ 2.112). It is interesting to note that these 

 groups of neurosecretory cells secrete endocrinokinetic hormones 

 that stimulate endocrine glands in both Crustacea and Insecta 

 (§ 4.21 ; Scharrer and Scharrer, 1954 b). 



not fused. The stomatogastric, or visceral, nervous system arises 

 from the stomodaeal ectoderm, and has paired nerves from the 

 tritocerebrum, a median frontal ganglion (Fr. gang), a branch to 

 the labrum (Lbr) and a recurrent nerve to the hypocerebral 

 ganglion (Hy) and the paired ventricular ganglia on the gut (near 

 Oes). Hormones are secreted by median (m.n.c), lateral (l.n.c.) 

 and suboesophageal neurosecretory cells (s.n.c); perhaps also by 

 cells in paired corpora pedunculata (C.ped.). Secretions from these 

 pass in two paired nerves to be stored in the corpora cardiaca 

 (CC), which arise from stomodaeal ectoderm (dashed arrow). 

 Hormones are also secreted by two paired glands that arise as 

 ectodermal invaginations: the corpora allata (CA from Mx i), 

 which migrate (dashed arrow) above the oesophagus, where they 

 receive axons from the corpus cardiacum (cf. Fig. 2-9); and the 

 VENTRAL GLANDS (Vent. gl. from Mx ii), which persist in primi- 

 tive insects, but form prothoracic glands (Proth. gl.) in most 

 other orders. (Based on two diagrams by Weber, 1949). 



