THE BIONOMICS OF AUSTRALIAN TAHANIDAE 45 



of the egg-mass. When about to hberate themselves the blade-Hke process (egg- 

 cutter) at the anterior end is pressed against the apex and drawn downwards along 

 the side m two or three deliberate strokes, which cause a rent in the shell sufficiently 

 large to permit the young larva to escape rapidly. 



Larval Development. Generally speaking, there is only an interval of a few minutes 

 between the appearance of the first and last larvae from a given batch of eggs. Some- 

 times, however, the interval is much longer, and this is especially the case with 

 large masses, in which, owing to their form, many of the eggs are concealed beneath 

 tiers of other eggs. One large mass from which all the larvae had apparently emerged 

 before noon (13th January) produced 110 additional larvae before 9 a.m. on the 

 following morning ; another produced about 600 larvae during the morning and 30 

 more late in the afternoon. 



In only one instance (5th April) was the dispersal of larvae observed under natural 

 conditions. On this occasion several very small larvae were gathered on the surface 

 of the pool (Plate I) in one dip of the scoop while searching for Anopheles, and upon 

 examining some twigs overhead an egg-mass was found from which larvae were then 

 dropping. The mass contained approximately 300 eggs, arranged in a single layer 

 eight or ten abreast, of which number about one-third had already hatched and 

 dropped into the water ; the balance emerged during the succeeding five or six minutes. 

 Upon reaching the water the young larvae were rather sluggish, but sufficiently active 

 to disperse by slow lashing movements, some remaining on the surface film, others 

 seeking the shelter of floating masses of algae. Some of these larvae were collected 

 and removed to the laboratory for examination and observation. 



In the laboratory the egg-masses were usually suspended over a shallow dish of 

 clean water, into which the young larvae dropped as they freed themselves from the 

 mass. For some hours they remained more or less quiescent on the surface, during 

 which period the first moult was accomplished. This process commences before, or 

 immediately after, the young larvae leave the egg, and is sufficiently advanced to be 

 seen under a low power five minutes later. Apparently the first moult is always 

 completed during the first six hours of larval life. As a number of larvae from one 

 egg-mass have been reared through all their stages to the perfect fly, the development 

 of these may be now recorded. While this batch was under observation a number of 

 other batches were available for study, and they supplied much information and 

 material for examination which could not have been obtained from the constantly 

 decreasing ranks of the original batch. 



The egg-mass from which the larvae were obtained was found partly evacuated 

 on 13th January (Locality 1); 110 young larvae emerged from it on the afternoon 

 and night of 13th-14th January and 105 of these comprised the original batch. 



First Instar. An accurate description of the young larva soon after it emerges 

 from the egg is somewhat difficult, owing to the fact that ecdysis has already com- 

 menced. When about five minutes old and after fixation in the usual way the young 

 larva measures about 1-40 mm. long by 0-28 mm. wide at the sixth segment^; the 

 segments appear to be withdrawn into each other ; the cuticle about to be cast off 

 envelopes the body loosely, excepting at the head, where it is firmly attached. The 

 surface is pale in colour and distinctly marked with longitudinal striae ; several 

 moderately long slender hairs are present about the middle of each segment ; there 

 are no short spine-like hairs fringing the anterior margin of the first three segments 

 (thoracic), such as occur on the fourth segment and in increasing numbers on the 

 fifth to the tenth segments. The anterior margin of the first two segments and the 

 anterior and posterior margins of the following seven segments appear to be banded, 

 but this appearance is due to characters on the cuticle beneath. The mandibles are 

 withdrawn into the head, but in cleared specimens they are seen to be short, curved 

 rods arising apparently in the anterior third of the first segment. The egg-breaker 



