VIII 



ARTHROPODA 



267 



map 



most recent and elaborate work on this subject has been done by 

 Poyarkoff (1910). He studied the metamorphosis of a beetle, 

 Galerucella ulmi, belonging to the family Chrysomelidae, i.e. to the 

 family to which Donacia and Doryphora also belong. Poyarkoff used 

 picroformol dissolved in alcohol at 60 C. to preserve the larvae, 

 cutting them open so as to allow the fluid to penetrate. 



The larva possesses nine visible abdominal segments, from which, 

 however, all trace of appendages has vanished. The thorax bears three 

 pairs of legs, each consisting of a basal 

 piece and of a single joint. The head 

 carries mandibles, two pairs of maxillae, 

 and a single pair of rudimentary ocelli. 

 The antennae are only represented by 

 knobs. The stomodaeum swells out into 

 a pharynx which is longitudinally ridged ; 

 behind this is a valve -like fold which 

 marks the beginning of the long mid-gut. 

 The mid -gut runs back to nearly the 

 posterior end of the body, then turns 

 forward till it reaches the front end of the 

 abdomen, and then turns backward again, mg 

 When it has reached as far back as the 

 end of the first limb there is a constriction 

 which separates it from the proctodaeum. 

 The proctodaeum consists of a portion 

 partly invaginated in a valve-like manner 

 into the mid -gut, followed by a second 

 section with six longitudinal folds which 

 is produced into a caecal pocket: this 

 section turns forwards. A third section 

 bends backwards again and is suddenly 

 constricted to form a fourth section, which 

 is the true rectum. From the caecal pocket 

 the four enormously long Malpighian 

 tubules arise ; they run nearly to the front 

 end of the body, then bend back and have 

 their terminal sections closely applied to 

 the third section of the proctodaeum. A 

 pair of salivary glands opens into the 

 buccal cavity. 



There are eight pairs of stigmata in the abdomen, one pair on the 

 mesothorax and a rudimentary pair on the metathorax. There is a 

 " brain " and twelve pair of ventral ganglia the first being the 

 suboesophageal ganglia. There is, of course, a dorsal tubular heart 

 in the abdominal region. Round the bases of the antennae and of 

 the legs there are imaginal discs which are slightly folded portions 

 of the ectoderm ; the cells forming these discs remain in an embryonic 

 condition and do not secrete cuticle. On the dorsal surfaces of the 



procl 



FIG. 212. Diagram of the 

 anatomy of the larva of 

 Galerucella ulmi. ( After 

 Poyarkoff. ) 



a, anus ; mgl, rag 2 , mg 3 , the first, 

 second, and third limbs of the mid- 

 gut ; map, Malpighian tubules ; o, 

 mouth ; proct, proctodaeum ; sal, 

 salivary gland ; stom, stomodaeum. 



