§ 2.113 SECRETORY CELLS FROM THE NERVOUS SYSTEM 29 



ing materials (§ 3.2) in many Decapoda. In the prawns, Leander 

 and Pefiaeus, it has been shown (Knowles, 1953 and 1954) that the 

 attached post-commissure organs are the swollen bases of nerves, 

 some motor fibres of which pass to dorsoventral muscles ; the two 

 nerves have a cross connection and contain many neurosecretory 

 fibres and secretory droplets and yield an active extract. Some of 

 the cell bodies are in the commissure (Fig. 2-Sc). 



The circumoesophageal connectives and the thoracic and 

 abdominal ganglia also yield extracts of varying activity, particu- 

 larly in forms such as Palaemonetes, in which the ganglia are not 

 fused in one mass. 



Pericardial organs 



In Decapoda and Stomatopoda there are some rather unusual 

 neurosecretory axons in the pericardium. They are supported by 

 larger nerve trunks and end blindly in networks of very fine 

 branches spread over the venous openings from the gills; they 

 are therefore exposed to the blood stream and appear to secrete 

 into it one or more chemicals that increase the rate of the heart 

 beat (§3.111). The position of the cell bodies of these pericardial 

 organs has not yet been found ; but recent evidence indicates the 

 presence of very fine granules in the fibrils, and experimental 

 evidence for their secretory activity is good. Similar structures 

 may also be present in Isopoda (Alexandrowicz, 1953). 



2.113 Neurosecretory systems and glands of Insecta 



The nervous system of Insecta has given rise to both neuro- 

 secretory cells and simple secretory cells which have lost any 

 morphological signs of their nervous origin. The former occur 

 within the central nervous system, mainly in the suboesophageal 

 ganglion and the brain, and the latter in the corpora cardiaca. 



The tritocerebral commissures and the circumoesophageal 

 connectives, though similar in form to those of crustaceans, have 

 not been shown to yield active extracts in insects. 



Suboesophageal ganglion 



Neurosecretory cells have been identified microscopically in the 

 suboesophageal ganglia of several insects, including some 



