Simidiidae 



403 



was induced to circulate by the action of a jet of compressed air released 

 from a glass jet introduced at the lower end of the wide-bore tube. The 

 wide-bore tube had an internal diameter of 1 to 2 cm., a tube of this 

 size being adopted after a number of trials with tubes of various diam- 

 eters as the one in which the most suitable current could be produced. 

 The capacity of the cylinders was about 5 liters and the compressed air 

 served to aerate the water as well as to create the current. The length 

 of the wide-bore tube varied, but this ap- 

 peared to be immaterial provided the open- 

 ing at the bottom was kept free of the debris 

 that eventually accumulated at the foot of the 

 cylinder, and the open end at the top was 

 sufficiently submerged to ensure effective 

 circulation of the water up the tube. The 

 tube for introducing the compressed air into 

 the system had an external diameter of 4 mm., 

 the actual jet being drawn out and slightly 

 slanted so as to project the stream of air 

 bubbles against the wall of the wide-bore 

 tube. The two tubes were held firmly to- 

 gether by means of rubber bands, and pieces 

 of rubber tubing were slipped over those parts 

 which were susceptible to injury and seemed 

 to require protection. 



The cylinders were first filled with tap 

 water and a culture of algae introduced by 

 the addition of about 250 cc. of water con- 

 taining a dense algal growth. This addition 

 tinged the water in the cylinder green, and 

 all that was subsequently necessary was to 

 replenish the stock of algae, when the green 

 tinge showed signs of disappearing. Some of 

 the water in the cylinder was then removed 

 and replaced by an equal amount of water containing the dense algal 

 culture. It was necessary that the jet should deliver a considerable and 

 steady quantity of air as it was found by experience that any but a 

 momentary interruption of the air supply served to disturb the conditions 

 in the cylinder to such an extent as to cause results fatal to the larval 

 population. 



Newly hatched first stage larvae were placed in the cylinder in large 

 numbers, and those which were carried by the current into the wide-bore 

 tube and contrived to secure a hold on the inner surface of the tube, 

 survived. On the average, about 20 imagines were reared in each from 



Fig. 71. — Diagrammatic sec- 

 tion of rearing apparatus for 

 Simulhim ornatntn. (After 

 Smart.) (x K). LBT, large 

 bore tube; JT, glass jet. 



