20 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



I have not examined the two younger stages, nor studied the transi- 

 tions between them, beyond observation that the cephalopharyngeal 

 skeletons are cast off and may be seen in the food. The following 

 notes all apply to third-stage larva?. 



The body is divided into 12 visible segments, though unless the 

 animal is fully extended one of the thoracic segments (numbers II 

 to IV) is apt to be overlooked. The mouth-opening is on the first 

 or head segment. This segment also bears a pair of small papillae, 

 known as antennae, and two pairs of small organs apparently sensory 

 in function. The sensory organs and their nervous connections are 

 figured by Keilin. The anus and posterior spiracles are on the twelfth 

 (eighth abdominal) segment. 



There are minute hooklets irregularly scattered over the surface 

 of the larva, but these are not easily seen except in eight bands of four 

 rows each that lie on the ventral surface of the larva, at the anterior 

 edge of each abdominal segment. In these bands the hooklets are 

 larger and darker in color than over the rest of the body. There are 

 several processes ("pseudopodia") on the last segment — usually three 

 with one or two papillae on each. From the upper posterior part of 

 this segment arise the posterior spiracular processes, each of which 

 bears a papilla on its upper surface. Each process ends in a chitinized 

 tube that has at its tip three 

 spiracular openings that are l \—^^^^^ ==^ — -^~zP 



surrounded b}^ very slender 

 outwardly directed chitinous 

 rays. When the larva is feed- 

 ing it lies buried in the food, 

 with only the tips of these ^ . . .,.,., 



, , Jig. 1. — .Interior spiracle of tnird-stage larva 



spiracular processes exposed of Drosophila funebris. 



to the air. The rays around 



the openings evidently serve to prevent the openings themselves from 

 sinking below the surface and thus cutting off the air-supply of the 

 larva, A large trachea runs forward from each posterior spiracle and 

 connects with the anterior spiracle of the same side. Each of these 

 tracheal trunks gives off numerous lateral branches, and not far from 

 the anterior spiracles there is a large cross-connection between the 

 two trunks. There is another cross-connection situated just anterior 

 to the posterior spiracles. The anterior spiracle of Drosoj>hila funebris 

 is shown in figure 1. The same type occurs in all drosophiline larvae 

 that I have seen. It is chitinous, and may be extruded somewhat. 



The cephalopharyngeal skeletons or ''jaws" of a few species are 

 showTi in figures 2, 3, and 4. These structures are jet black, except 

 for the more posterior processes, w^hich are brownish. The names of 

 the parts that appear in figure 2 are from de Meijere's accoimt of 

 D. ohscura. All the parts shown in these figures are paired, and the 



