270 



INVEETEBEATA 



CHAP. 



old, appearing as a pair of ectoderrnic invaginations at the bases of 

 the first maxillae. 



The Malpighian tubes undergo curious changes. They are lined 

 in the larva with large granular cells, and at intervals between these 

 cells small replacement cells are seen. When the metamorphosis 

 begins these small replacement cells multiply, become fusiform, and 

 pass inwards till they form a string occupying the axis of the tube. 

 The string becomes hollowed out and forms the lining of the adult 

 Malpighian tube, whilst the cells which formed the lining in the 

 larva gradually liquefy (Fig. 215) and their remains are removed by 

 amoebocytes. 



FIG. 214. Sections of the epithelium of the 

 mid-gut iu the pupa of Ualerucetta idmi 

 showing the changes undergone by the 

 metamorphosis into the adult condition. 

 (After Poyarkoff.) 



A, from the gut of a pupa four days old. B, 

 from the gut of a pupa five days old. C, from the 

 gut of a pupa seven days old. a.end, adult endo- 

 derin ; p.end, pupal endodenn. 



FIG. 215. Portions of the Malpighian 

 tubes of a larva and a pupa of Galeru- 

 cella ulmi. (After Poyarkoff.) 



A, tube of larva. B, tube of larva just 

 beginning to pupate, l.n, larval nuclei ; p.n, 

 pupal nuclei. 



Finally, many of the muscles of the larva disappear; first the 

 striation is lost and the cytoplasm forms a homogeneous mass, then 

 the nuclei multiply and become dispersed through it, and then the 

 whole mass is attacked and devoured by amoebocytes. The corre- 

 sponding adult muscles are formed by the growth and elongation of 

 masses of small oval mesodermic cells which are attached to the 

 inner sides of the corresponding "imaginal discs" (Fig. 216). In the 

 case of some larval muscles, however, such as the powerful adductor 

 mandibuli, a portion of the cytoplasm persists and is not eaten by 

 amoebocytes, and its nuclei multiply and it becomes converted into 

 the fibres of the adult muscle. The changes in the heart and in 

 the nervous system were not examined by Poyarkoff. 



Poyarkoff did not study the development of the wings in 



