THE ANATOMY OF THE LARVA 45 



position without being made to revolve on its axis under 

 the influence of the strokes of the tail. In addition to 

 these principal tufts, other smaller but also pedunculated 

 tufts spring from the sides of the terga of the segments, 

 the characters of which should be accurately noted in 

 describing species, as it is probable that their form, number 

 and position, may yield good specific characters. The great 

 preponderance of the mesothoracic segment is already well 

 marked, though not to anything like the same extent as 

 in the imago. 



Proceeding with the examination of the living larva, the 

 first thing that catches the eye in the thorax are four pairs 

 of what at first sight appear to be pigment spots. A little 

 watching, however, suffices to show that these are not really 

 external markings, but internal organs seen through the 

 transparent carapace, and that their position is constantly 

 altering under the action of the surrounding thoracic 

 muscles, and of the pulsations of the dorsal vessel. Ex- 

 amined with a somewhat higher power, they are seen to be 

 glandular bodies of a sacular form, lined with secretory 

 cells, their cavities being filled with a clear fluid, holding in 

 suspension a quantity of deep brown granular matter. These 

 glands are connected with the upper end of the intestine, 

 and are probably hepatic in function. In the dead, or 

 preserved and mounted larva, they soon become invisible, 

 owing to the discharge of the contained brown matter into 

 the intestine. 



These glands are arranged in two sets, an internal and 

 an external, the former of which consists of two glands 

 placed so closely together as often to look like a single 

 mass, and situated nearly in the middle of the thorax, close 

 to the intestinal canal. The other two pairs are placed at 

 a distance from the intestine, in the corners of the pro- 

 and metathorax respectivel3^ In the middle line the dorsal 

 vessel can be seen pulsating, the action being rather that 

 of a peristaltic wave than a true systole, the heart being 

 here a long, valved tube, corresponding rather to an aorta 

 than to a heart in the usual acceptation of the word. 



More or less in the middle line, too, its coarser image 



