58 ABIOLOGYOFCRUSTACEA 



head. A great deal more is known about hormones in the decapods. 



The method of establishing that an organ is the site of hormone 

 production is to remove the organ, observe the resulting condition 

 of the animal, and then restore its normal functions by injections 

 of extract from the same organs or bv implanting such organs in 

 the bodv. Confirmatory methods include staining the organ in 

 such a way that will show if it is secretory, and by observations 

 on the rate of change of a process as the organ regenerates after 

 removal, but these cannot replace the method of ablation followed 

 by restoration of function. 



Using methods similar to those described above it has been 

 shown that the nervous system of the Crustacea contains the most 

 important sites of hormone production. 



In general plan the nervous system consists of a brain, lying 

 above the oesophagus, connected to a chain of ganglia which lie 

 beneath the gut. The first ganglion in the chain is the sub- 

 oesophageal ganglion (fig. 29). The brain and the sub-oesophageal 

 ganglion give off nerves to the antennae and the mouthparts. The 

 two nerves connecting the brain with the sub-oesophageal ganglion 

 are known as the circum-oesophageal commissures. In fig. 29 the 

 main sites of hormone secretion are indicated bv the dark cells 

 which have fibres leading out to storage and releasing sites. 



The eyestalks house a complex arrangement for the production 



POST OESOPHACeAL 

 COMMISSURE 



POST COMMISSURAL 

 NERVE 



SUB OESOPHAGEAL 

 CANCUON 



Fig. 29. Diagram of the front part of the nervous system of a 



decapod, to show the location of some important centres of 



hormone secretion. 



