§ 2.112 SECRETORY CELLS FROM THE NERVOUS SYSTEM 25 



the commissures and connectives arising from the brain, and 

 extracts showing hormonal activity have been obtained from them 

 (§ 3.223); but the natural point of release for their secretions into 

 the blood stream is uncertain. It may be the post-commissure 

 organs (Knowles, 1953). 



A fourth system has been found in the pericardial organs of 

 various decapod crabs and of Stomatopoda; these also yield an 

 active extract (§ 3.11), but a natural secretion has not been fully 

 established. 



Brain, ganglionic- X-organ and sinus gland 



Some of the neurosecretory cells, that release their secretion 

 in the sinus gland, have their cell bodies in the protocerebrum 

 of the brain and others in its extension into the terminal medulla 

 of the optic lobe. The details vary for different orders and species. 

 For instance, in the crab, Gecarcinus, the cells extend from the 

 protocerebrum into the deutero- and tritocerebral lobes of the 

 brain (Fig. 2-5^-^; Bliss and Welsh, 1952). 



The relatively large group of neurosecretory cells (Fig. 2-7) that 

 lies in the terminal medulla is best known as the ganglionic- 

 X-organ (pars ganglionaris X organi of CarHsle, 1953). 



It is important to remember the positions of these neuro- 

 secretory cells in experimental work. Removal of the whole 

 eyestalk removes the ganglionic-X-organ but leaves the cell bodies 



outer part of the optic stalk and nerves to the retina (R) (after 

 Bliss and Welsh, 1952); (c) post-commissure organ (Post, com.) 

 of a prawn, Leander, attached to tritocerebral commissure and 

 having neurosecretory granules, (after Knowles, 1955). Protocere- 

 brum (PRO), carrying optic lobes (OP), and deuterocerebrum 

 (DEU), both joined by internal commissures, not shown; tritocere- 

 brum (TRI) with its commissure (Tr. com.) behind oesophagus 

 (Oes); circumoesophageal connectives (Conn.) join brain longi- 

 tudinally to fused suboesophageal (SUBOES) and thoracic ganglia 

 (THOR). Eyestalk contains continuation of optic lobe ending in 

 terminal medulla (MT) with ganglionic-X-organ (GXO), and 

 neurosecretory axons that end in sinus gland (SG) on internal 

 medulla (MI); the external medulla (ME) also has some neuro- 

 secretory axons. Nerve roots to antennae (A i and A ii), viscera 

 (Vis), mandible (Mdb), maxillae (Mx i and Mx ii) and thoracic 

 appendages (Th i, etc.). 



