PHYSIOLOGY AND BEHAVIOR OF THE ARTHROPODA 



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Figure 17.2. Neurosecretion. The neuron produces secretion granules in the cell 

 body (left) that are stored in the expanded tip of the axon, where they may also be re- 

 leased (right). If the axon is cut, material accumulates at the cut (below). 



a homogeneous group of pale blue cells. Actually, however, these are 

 not gland cells at all, but the expanded tips of bundles of axons. The 

 cell bodies of these axons lie some distance back on the proximal sides 

 of the optic ganglia (Fig. 17.3) in the x-organ. Cells of the x-organ 

 resemble ordinary secretory cells, with a granular cytoplasm of variable 

 appearance and large nuclei. The secretions appear as bluish granules 

 that move very slowly through the axons to their tips. Thus the sinus 

 glands are merely storage areas for the hormones (or their precursors) 

 which are produced in the x-organs. Some axons from the x-organs 

 extend, not to the sinus glands but to other structures in the region. The 

 nature and function of these smaller structures was previously misun- 

 derstood but they are now known to be expanded axons with endocrine 

 activity. Presumably this structural arrangement permits hormones to be 

 elaborated under one set of local conditions and to be released at a 

 distance where conditions are different. 



-Rctinulae of 

 compound, eye 



Sinus oland 





Conn.<2.ctiorL 

 with brain - 



-Portions of _ 

 optic (SajaOlion. 



-X- OTgZLn 



Figure 17.3. Eyestalk of the crab with the skeleton removed, showing sinus gland 

 and x-organ. (After Passano.) 



