270 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



moving mucli more decidedly than the tergal portion of the abdomen. 

 When the pleural portion of the abdomen is forced out, the soft pleural 

 membranous region under the fore and hind wings contracts, as does 

 the tympanum and the membranous portions at the base of the hind 

 legs. When the tergum or dorsal portion of the abdomen falls, and the 

 pleurum contracts, the spiracles open -, their opening is nearly but not 

 always exactly co-ordinated with the contractions of the pleurum, but 

 as a rule they are. There were 65 contractions in a minute in a locust which 

 had been held between the fingers about ten minutes. It was noticed 

 that when the abdomen expanded the air-sacs in the first abdominal 

 ring contracted. This would indicate that the air rushes into the spir- 

 acles during the contraction of the abdomen, and that the air-sacs are 

 not refilled until the spiracles are closed ; thus the air in the air-sacs is 

 perhaps constantly changing.^^ * 



The locust an aeronaut. — It is evident that the enormous powers of 

 flight possessed by the locust, especially its faculty of sailing for many 

 hours in the air, is due to the presence of these air-sacs, which float it 

 up in the atmospheric sea. Other insects with a powerful flight, as the 

 bees and flies, have well-developed air-sacs, but they are less numer- 

 ous. In a grasshopper (Truxalis), as figured by Marcel de Serres, the 

 air-sacs are as numerous as in the normal Acrydii^ but they are more 

 developed in the locust family {Acrydii) than in the green grass-hoppers 

 {Locustarice): 



It will be seen that, once having taken flight, the locust can buoy 

 itself up in the air, constantly filling and refilling its internal buoys or 

 balloons without any muscular exertion, and thus be borne along by 

 favorable winds to its destination. It is evident that the process of 

 respiration can be best carried on in clear, sunny weather, and that when 

 the sun sets, or the weather is cloudy and dami^^ its powers of flight are 

 lessened, owing to the diminished power of respiration. 



The male reproduetwe system. — As observed in C. spretus and more care- 

 fully in G. femur-ruhrum, each testis is closely united to the other, so 

 as to form a single mass of tubular glands, arranged vertico -obliquely, 

 and interpenetrated by simple and dilated tracheae. The mass rests on 

 the intestines, andas situated in the third, fourth, and fifth abdominal 

 segments. The anterior end of the testicular mass is rounded and held 

 in place by a broad, thin band, one on each side ; two similar bands are 

 situated a little behind the middle of the mass. 



From the under side, and a little in advance of the middle of the mass, 

 two straight small ducts, as long as the testicular mass, pass obliquely 

 to the sides of the body, at the posterior end of the seventh segment 

 of the abdomen ; these are the vasa deferentia. Each vas deferens with 

 its mate forms a convoluted mass of tubes, comprising 20 folded bundles 

 {epididymis of Dufour), and two single, long, convoluted tubes, the 

 vesieulcc seminales. 



''^ It was noticed in a species of Gryllus or cricket {G. negUctusI) that there are no air-sacs, but dilated 

 tracliese somewJiat like those in Caloptenus. It is evident that in those Orthoptera which do not take 

 long flights there is no need of air-sacs. They are most developed in those insects which fly most. 



