H. M. Morris 95 



The heart has a small posterior chamber, provided with a pair of 

 lateral openings by means of which the blood enters. These openings 

 are closed by means of valves when the heart contracts, thus forcing the 

 blood along the dorsal vessel. The latter is very thin walled, the nuclei 

 of the cells of which it is composed bulging inwards into the vessel. The 

 blood is a colourless fluid containing relatively large colourless corpuscles 

 which are usually oval in shape. 



Nervous System. The nervous system is similar to that of the full- 

 grown larva. The supraoesophageal ganglion lies in the front of the first 

 segment with the suboesophageal ganglion beneath it. The first thoracic 

 ganglion lies in the posterior region of the first segment, the second is 

 similarly situated in the second segment, while the third ganglion lies 

 rather more forward in the third segment. The eight abdominal 

 ganglia lie in the posterior half of their segments, except the eighth, 

 which is in the front of the eleventh segment, 



(b) Second stage larva. 



The larvae passed into the second stage after nineteen days, under 

 laboratory conditions. 



This larva is much more like the full-grown larva in external appear- 

 ance than is the newly hatched form. 



The head does not appear relatively so large, while the long setae on 

 the body have disappeared, the body now bearing processes similar to 

 those of the fully grown larva. The cuticle also bears scale-like structures 

 similar to those of the full-grown larva, but somewhat smaller. The 

 spiracles on the last segment are larger but each has still only a single 

 opening. A smaller pair of spiracles is situated on the first segment as 

 in the full-grown larva, and there is also a still smaller pair of spiracles 

 on the tenth segment. From this latter pair of spiracles the outwardly 

 directed branches from the main longitudinal trunks in that segment 

 take their origin. The tracheal system is similar to that of the first 

 stage larva, but it has more numerous branches. 



The mouthparts are very little different from those of the first stage 

 larva, but are slightly more like those of the full-grown larva. 



(c) Fully grown larva. 



(a) External Form. The larva is 10 to 11 mm. long by 1-2 to 

 1-3 mm. wide and its thickness is a little less than its width. Of this 

 length about -9 mm. is the length of the head, which is of slightly less 



