. io6 The Fly of Chironomiis 



in insects whose females bear an ovipositor. Similar 

 appendages are found in Lepidoptera, Trichoptera, and 

 Epliemeridae. The styles of the cockroach are borne 

 upon the same segment. The median dorsal spine 

 (suranal plate of some authors) has been explained as 

 an undeveloped tenth segment. 



Nervous The followiug features distinguish the nervous system 



system. o o j 



of the fly from that of the larva : — 



The brain and sub -oesophageal ganglion, now enclosed 

 in the head, are more widely separated from the rest of 

 the nerve-cord. Each thoracic ganglion lies in its own seg- 

 ment. The first abdominal ganglion is closely united with 

 themetathoracic,and the seventh and eighth become fused. 



We may perhaps say that there is some amount of 

 decentralization during the transformation of Chironomus. 

 Certain families of Brachyceran Diptera, such as Stratio- 

 myidae, Tabanidae, Syrphidae, Conopidae, and Acalypte- 

 rate Muscidae, exhibit the same process of decentralization, 

 the ganglia becoming separated during metamorphosis. 

 In Calypterate Muscidae, Oestridae, Hippoboscidae, and 

 Nycteribiidae the thoracic and abdominal ganglia, which 

 were already fused in the larva, remain so. Decentrali- 

 zation may also occur in Coleoptera. Thus in most 

 Lamellicorns, as well as in some Curculionidae and 

 Scolytidae, the ganglia of the ventral cord are so closely 

 a23proximated in the larva as to appear like a single 

 ganglionic mass, while after transformation the thoracic 

 ganglia at least are separated, and double connectives 

 form between them. 



Alimentary In the fly the whole alimentary canal is considerably 

 reduced (fig. 80). The salivary glands may shrink to two 

 minute and structureless membranous sacs ^, the epithelial 

 cells of the stomach almost completely disappear (fig. 113), 

 and the rectal folds, to be described below, are the only 

 indication of a structure more complex in the alimentary 

 canal of the fly than in that of the larva. 



It is evident that Chironomus does not feed in the winged 



' In another species this shrinkage of the salivary glands was not found 

 to occur. 



