r 



ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 193 



con^^regates in great numbers on a small area wheie by repeated bites it 

 produces a practically constant state of irritation. Old, poor-conditioned 

 and sickly stock suffer most. Hair-colour appears to make no appreci- 

 able difference, but some individuals are not molested. Goats are 

 seldom attacked : dogs, pigs, sheep, and kangaroos are apparently immune. 

 Horses, cattle, and buffaloes are the most frequent victims, but the 

 characteristic sores are less severe on the buffalo, pi'obably because of its 

 thicker skin and its habit of standing up to the neck in mud or water 

 for long periods. 



The eggs of Lyperosia are usually deposited in the fresh droppings 

 of cattle and horses ; accumulated heaps of stable-manure are not 

 favourable to their development, but milking yards are great centres of 

 infection. The eggs are pale Ih'owu in colour, and are laid singly on the 

 wet surface of the dung, oviposition taking two to four minutes. The 

 young larvae descend into the dung and pupation takes place there. In 

 those reared under laboratory conditions the life-cycle was completed on 

 an average in 1(V.) hours. The species is believed to have been intro- 

 duced into Australia since 1824 with some of the earlier importations 

 from the East Indies of buffaloes, cattle and horses. Its distribution 

 coincides, on the whole, with the range of the introduced buffaloes. 

 Few indigenous birds pick food from dung, and Lyperosia has not many 

 natural enemies except some species of ant which gathers the eggs, and 

 a small Hymenopteron which captures the flies while feeding or at rest. 



Circulation of the Blood in Insects.* — F. Brochet has followed 

 up his paper on the circulation of the blood in the larva of Dyticus 

 marginalis by a study of Agrionid larva?. These are particularly well 

 adapted for study because they are transparent after moulting, and can 

 be kept so in clean water. Before examination under the microscope 

 they were not fed for twenty-four hours, so that the alimentary canal 

 should not be opaque. In the Agrionid larva, as in Dyticus, the dorsal 

 vessel functions mainly as an inspiratory pump ; it tends continually to 

 drain the abdominal cavity, and thus indirectly acts as exhauster for all 

 the blood in the body. The circulation of blood in the wings is effected 

 by two special pulsating oi'gans in the meso- and meta-thorax. In the 

 legs the mechanism is quite different, the circulation of the blood in 

 them depending on the respiratory action. Certain structural and 

 physiological facts were clearly observed : the presence in the thorax 

 of the larv« of Aeschna of two transverse diaphragms provided with a 

 ■ sphincter through which the oesophagus passes ; the presence in the 

 femur of a true blood-vessel ; the presence in the tibia of a longitudinal 

 partition pierced by two small orifices ; and the presence of two pulsat- 

 ing organs in the meso- and meta-thorax. It was possible to observe, 

 especially in Agrionid larvae, the relation between the movements of 

 rectal expulsion and the gush of blood into the femur, and the fact that, 

 in anaesthetized insects, the blood flows towards the abdomen and towards 

 the dorsal vessel under negative pressure, therefore as a result of an 

 inspiration, and not under positive pressure, as would be the case if it 

 Tvere a question of propulsion. 



♦ Arch, de Zool. Exp6r. et Gen., Ivi. (1917) pp. 445-90. 



