ENEMIES OF APHIDES. 35 



as the oesophagus (Fig. i, <?, PI. III.). The transverse muscles 

 shown in Fig. 4, PI. III., are sheathed by longitudinal bands, as 

 shown at ^, Fig. i. Together they control the opposition of the 

 upper and lower blades of the piercing organ, and by causing 

 rhythmic contractions at the base of the pharynx cause it to act as 

 a powerful suctorial organ. On either side of the head are three 

 long muscular bands, arising from the epidermis and inserted 

 into the framework of the piercing organ, as shown at d^ d, Fig. i, 

 PI. III., which control the forward and retractile movements with 

 great completeness. 



The Digestive Organs of the Larva. 



An outline of the alimentary system has been already given in 

 the last section in explanation of the first figure of PI. XV. (Vol. 4). 



The most notable features are the extensive salivary glands 

 and the great capacity of the stomach. The anterior portions of the 

 former are shown at n, PI. III., Fig. i. Each consists of a blind tube 

 of delicate, unorganised membrane, lined with large, nucleated, epi- 

 thelial cells. The tube is greatly enlarged at its remote or blind 

 end, and after doubling upon itself for half the length of the larva is 

 lost at its narrow end among the muscles surrounding the pharynx. 

 The outer surface is smooth, and the nature of the fluid secreted 

 differs from that secreted by similar organs in the imago, inasmuch 

 as it does not coagulate in water. The secretion of the larva is 

 probably non-albuminous, or at most only very slightly so. 



The structure of the stomach presents no peculiarities suffi- 

 cient to occupy our attention here. Under an amplification of 

 1,000 diameters, it presents no appearance of organisation beyond 

 faint traces of striation here and there, showing the existence of a 

 muscular coat. 



One other point may be noted, which may possibly be of value 

 in the future classification of the larvae — that is, the colour of the 

 hepatic vessels. Thus, in certain larvae, and especially in the 

 larva of Syr. limiger, these vessels are yellow to brown. In another 

 group of larvae, distinguished by a clear pink stripe down the 

 centre of the back, they are green, while in some very transparent 

 larvae, which I have not succeeded in rearing, they are of a deep 

 crimson. 



