164 THE COCKROACH: 



most frequent complications arises by the differentiation of this 

 sheet of vertical fibres into distinct muscles, repeated in every 

 segment, and becoming more and more separated as the sterna 

 increase in length. (See the tergo-sternal muscles of the 

 Cockroach, fig. 36, p. 76.) Special inspiratory muscles occur in 

 Hymenoptera, Acridiidoo, and Phryganidoc. 



10. The abdominal respiratory movements of Insects are 

 wholly reflex. Like other physiologists who have examined 

 this side of the question, the writer finds that the respiratory 

 movements persist in a decapitated Insect, as also after destruc- 

 tion of the cerebral ganglia or oesophageal connectives ; further, 

 that in Insects whose nervous system is not highly concentrated 

 (e.g., Acridiidic and Dragon-flies), the respiratory movements 

 persist in the completely-detached abdomen ; while all external 

 influences which promote an increased respiratory activity in 

 the uninjured animal, have precisely the same action upon 

 Insects in which the anterior nervous centres have been 

 removed, upon the detached abdomen, and even upon isolated 

 sections of the abdomen. 



The view formerly advocated by Faivre, that the metathoracic 

 ganglia play the part of special respiratory centres, must be 

 entirely abandoned. All carefully performed experiments on 

 the nervous system of Arthropoda have shown that each 

 ganglion of the ventral chain is a motor centre, and in Insects 

 a respiratory centre, for the somite to which it belongs. This 

 is what Barlow calls the "self-sufficiency " of the ganglia. 



The writer has made similar observations upon the respiration 

 of Spiders and Scorpions ; * but to his great surprise he has been 

 unable either by direct observation, or by the graphic method, 

 or by projection, to discover the slightest respiratory movement 

 of the exterior of the body. This can only be explained by 

 supposing that inspiration and expiration in Pulmonate 

 Arachnida are intra-pulmonary, and affect only the proper 

 respiratory organs. The fact is less surprising because of 

 the wide zoological separation between Arachnida and 

 Insects. 



* De 1'absence de mouvements respiratoires perceptibles chez les Arachnides 

 (Archives de Biologie de Yan Beneden et Van Bambeke, 1885.) 



