72 



The Larva of Chironomus 



lieart. lu a larva of one of the larger species of Chiro- 

 nomus the heart lies in the eleventh post-cephalic 

 segment, and forms a single chamber with a muscular 

 and rhythmically contractile wall. A pericardium can 

 be seen in transverse sections which pass through the 

 hinder part of the heart ; elsewhere it is deficient. Two 

 pairs of ost'ia or lateral inlets, of which the hinder pair 

 are the larger, lead from the pericardium or from the 

 body-cavity into the heart. The aorta leads from the 



Fig. 5.^ — Heart of larva, ventral 

 view, showing muscles (w) and con- 

 nective-tissue fibres, which hold it in 

 its place {ct.f). 



Fig. 54. — Heart of larva, 

 dorsal view, showing ostia 

 and muscles of wall. 



heart to the head, lying above the alimentary canal. It 

 passes beneath the commissure of the supra-oesophageal 

 ganglia, and becomes enlarged further forward. A pair 

 of rather large aortic valves guard the passage from the 

 heart to the aorta ; in front of these neither valves nor 

 ostia are to be found, at least in young larvae. We have 

 several times observed small bodies, which may be 

 ganglia, set alternately on opposite sides of the aorta. 



