INSECTA. 



973 



Fig. 430. 



Fig. 431, 





Alimentary canal of Sphinx Kgtutri. 



the pollen in the canal leading to the bag, in 

 the oesophagus, and in the stomach itself. A 

 gizzard does not exist either in the Diptera or 

 Lepidoptera, but there is a slight rudiment of 

 it in the Sphinx (i). The stomach of Lepidop- 

 tera is in general short, oval, or a little elon- 

 gated (/c), and always very muscular, and as 

 in other insects, the hepatic vessels (/>) enter 

 .at its pyloric extremity (</). The ilium (/) is of 

 considerable length. In the Sphinx it makes 

 seven folds, and then passes straight to the 



Alimentary canal of Pontia brassicce. 



colon, which is developed anteriorly into a very 

 large ccecum (;/z), and terminates in a narrow 

 short rectum (n). Throughout its whole course 

 it is covered by the hepatic vessels. In the 

 Pontia brassier (jig. 431), the digestive sto- 

 mach is preceded by a very muscular and 

 transversely banded portion of canal resembling 

 the stomach of Hymenoptera. It is in the pre- 

 cise situation of the gizzard in other orders, and 

 appears to be the representative of that part in 

 this insect. The true stomach is long and oval, 

 and the ilium is longer than in the Sphinx, and 

 the ccecum, colon, and rectum are all distinct. 

 In the Diptera the alimentary canal is usually 

 very long, and is scarcely at all shorter in the 

 carnivorous than in the omnivorous feeders. 



Appendages of the canal. The first of these, 

 the salivary glands, are very frequent in most 

 of the orders, but vary greatly in form and 

 number. In Lepidoptera they are simple 

 elongated tubes (h\ which extend into the 

 thorax and are convoluted beneath the oeso- 

 phagus and anterior portion of the alimentary 

 canal. In the larva they constitute the silk 

 vessels, and empty themselves by a single duct 

 through the spinneret on the floor of the 

 mouth. They are formed of three por- 

 tions; first, the excretory, which is thin and 

 transparent, and is gradually enlarged as it 

 passes backwards along the body; second, the 

 apparently secretory portion of the organ, which 

 is of an elongated cylindrical form, externally 

 transversely marked as if formed of muscular 

 fibres, and internally covered with a vast 

 number of rounded glandular bodies, as we 



