256 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



ment proceeds, attaining the region of the metathorax. On the bhnd 

 end of the proctodaeum the buds of four Malpighian tubules appear 

 which reach a considerable length before the hatching of the insect. 

 They form as solid strands which later acquire a lumen. The reproduc- 

 tive organs are not recognizable as such until the revolution of the 

 embryo. What Melnikow (1869) considered to be the germ cells at the 

 posterior end of the egg was probably the mass of symbionts. After 

 revolution a small ventrally located anlage of the genital ducts is formed 

 which remains at this stage of development until the first larval instar. 

 The visible differentiation of the germ cells apparently occurs in larval life. 



Fig. 180.- — Pediculus. Sagittal section of caudal end. {am) Amnion, {mge) Mid-gut 

 epithelial rudiment, {prod) Proctodaeum. {ser) Serosa. 



The mouth parts in the fully developed embryo, according to Scholzel 

 (1937), are readily homologized with those of the adult. The ventral 

 "bristle," provided with a lumen, is developed from the second maxillae. 

 From the hypopharynx there is developed the "dorsal bristle" of Vogel 

 or sucking tube of Sikora and a ventrally located thin sclerotized tube, 

 designed as the "middle bristle" by Vogel or the "salivary duct" by 

 Sikora. Dorsad of the bristles is the anterior part of the pharynx with 

 its dilator muscle. The first maxillae are, according to Scholzel, greatly 

 reduced. Fernando (1933), however, considers the dorsal stylet as 

 developing from the first maxillae, whereas the salivary duct alone is 

 derived from the hypopharynx. 



MALLOPHAGA, THE BITING LICE 



The eggs of the Mallophaga are uniformly smaller than those of the 

 Siphunculata and are rather variable in form. The species parasitic on 

 mammals resemble those of the Siphunculata in form and manner of 

 attachment to hair, whereas those which live on birds are obviously 

 modified to adapt them to a different environment. The eggs of most 



