)32 



BAKER : HYDROBIUS FUSCIPES. 



are also supplied from the head to the oesophagus. The three 

 thoracic ganglions are globular in shape and send oJ5f nerves to the 

 legs as well as the segments. The abdominal ganglions, which are 

 seven in number, are oval, with the exception of the last one. 

 Nerves are supplied from each of these ganglia to the segment in 

 which it is placed. All these ganglia are united to each other by 

 a double cord. In the perfect insect the abdominal ganglia coalesce, 

 and the optic nerves are not separate but form one nerve trunk to 

 each of the two compound eyes; in other respects the structure of 

 the nervous system is the same in larva and imago. 



The alimentary canal (Fig. 7) consists of little 

 more than a long tube running the whole length 

 of the animal, and consisting of three divisions — 

 the oesophagus, the stomach with its Malpighian 

 tubules attached at each end, and a short 

 intestine. 



The circulatory system can be seen very 

 plainly in a young larva. It consists of a long 

 vessel, constricted at each segment, which pumps j 

 the circulatory fluid forward through the body, ^ 

 bathing all the organs. ! 



When the larva is ready to pupate it crawls up | 

 the bank side, about six inches above the water, / 

 and there makes a circular burrow about a quarter j 

 of an inch below the surface (Fig. 8) but connected \ 



with the air by a small aperture. Here it remains \ 



for from three to six days and then turns into ( 



the pupa. The pupa is perfectly white and 

 exhibits all the parts of the perfect insect in the 

 usual shrouded form (Fig 9). Very long spines 

 project from the prothorax, and the whole body of Fig. 7. 



., .11 1 ■ 1 • 1 • , ■ Alimentary cana 



the pupa on the dorsal side is covered with spines 



Nov. 1894. 



Fig. 8. Pupa in situ. X2 



