EFFECTS OF INJURY TO THE BRAIN 



245 



in insects a respiratory centre, for the somite to which it belongs " 

 (Miall and Denny's The Cockroach, p. 164). 



The last pair of abdominal ganglia serve as tne nervous centre 

 of the nerves sent to the genital organs. 



The recurrent or stomatogastric r\erve, which, through the medium 

 of the frontal ganglion, regulates digestion, has only a slight degree 

 of sensibility ; the insect remains quiet even when a powerful allure- 

 ment is presented to the digestive tract (Kolbe). 



Faivre states that the destruction of the frontal ganglion, or a 

 section of the commissures connecting it with the brain, puts an end 

 to swallowing movements ; on the other hand, stimulation results 

 in energetic movements of this nature. 



Yersin, by cutting through the commissure in different places, and 

 thus isolating the ganglia of the nervous cord of Gryllus campestris, 

 arrived at the following results : 



1. The section of a nerve near its origin rendered the organ sup- 

 plied by this nerve incapable of performing its functions. 



2. If the connectives between two ganglia, i.e. the second and third 

 thoracic ganglia, are cut through, the fore as well as hinder parts of 

 the body retain their power of motion and sensation ; but a stimulus 

 applied to the anterior part of the body does not pass to the hinder 

 portion. 



3. Insects with an incomplete metamorphosis after section of the 

 connectives are not in every case unable to moult and to farther 

 develop. 



4. If only one of the two connectives be cut through, the append- 

 ages of the side cut through which take their origin between the 

 place injured and the hinder end of the body, often lose sensation 

 and freedom of motion, or the power of coordination of movements 

 becomes irregular. Sometimes this is shown by an unsteadiness in 

 the gait, so that the insect walks around in a circle ; after a while 

 these irregularities cease, and the movements of the limbs on the 

 injured side are only slightly restrained. By a section of both con- 

 nectives in any one place the power of coordination of movements is 

 not injured. 



5. The section of the connectives appear to have no influence on 

 nutrition, but affects reproduction, the attempt at fertilization on the 

 part of the male producing no result, and the impregnated female 

 laying no eggs. 



6. Injury to the brain, or to the suboesophageal, or one of the 

 thoracic ganglia, is followed by a momentary enfeeblement of the 

 ganglion affected. Afterwards there results a. convulsive trembling, 



