148 MEDICAL ENTOMOLOGY 



and organs of the abdomen, and sends a nerve cord to the ganglion 

 immediately posterior to it. 



The actual conditions to be met with in the Diptera are well 

 exemplified by a comparison of Anopheles, Tabanus (Plate XXVII, 

 fig. 1) and Musca (fig. 4, ibid.). In each of these the brain forms a 

 compact mass which is pierced by the alimentary tract and gives off a 

 large trunk on each side posteriorly. These nerve cords lie at first external 

 to the oesophagus as it emerges from the brain, but as they converge 

 to join one another they come to lie below it. In each of these forms 

 the thoracic ganglia are fused with one another to form a large mass which 

 lies in the middle ventral line in the anterior part of the thorax, but well 

 marked differences are seen as regards the abdominal ganglia. In Ano- 

 pheles these are six in number, and are well separated from one 

 another. In Tabanus five abdominal ganglia can be distinguished, 

 but they are set close together, looking like a string of small white beads. 

 In Musca the abdominal ganglia are fused with the thoracic to 

 form a large compound ganglion, from which many fine nerves pass 

 backwards to the abdomen. There is thus a well-marked relation 

 between the concentration of the nervous system and specialization in 

 other directions. 



The ganglion cells are of considerable size, and show up well 

 in sections stained with haematoxylin, so that the separate parts 

 of a compound ganglion can be readily recognized. In the brain 

 there are certain curious and highly complex structures, known as 

 the ' mushroom bodies ', which stain brightly with eosin, and are con- 

 spicuous in sections of the head. These are connected with many 

 commissures and tracts within the substance of the brain ; for an 

 account of them the reader is referred to Berlese's work. 



LITERATURE 



ANNETT, H. E., DUTTON, J. E. Report of the Liverpool Expedition to Nigeria, part 

 and ELLIOT, J. H. ii. Thompson Yates Laboratories Reports, Vol. iv, 



Part i, 1901 . 



Contains an account of the proboscis and sucking 

 apparatus of Anopheles costalis, with numerous 

 coloured drawings. 

 BERLESE, A. Gli Insetti. Vol. i. Embriologiae Morphologia. Societa 



Editrice Libraria, Milan, 1909. 



A book of 1004 pages, Crown quarto size. It deals 

 with all orders of insects, is very well illustrated, 

 and contains a large bibliography, with references 

 to all the older papers. 



