432 GENERAL ZOOLOGY 



Examples : Pulex irritans, human flea ; Ctenocephalis felis, cat 

 flea; Ctenocephalis canis, dog flea; Xenopsylla cheopis, rat flea, 

 carries the germ of bubonic plague. 

 Order Hymenoptera (Membrane-winged). Bees, wasps, ants, 

 sawflies, and ichneumon flies. Two pairs of wings with 

 reduced venation; the anterior pair larger than the posterior. 

 Mouth parts are for chewing or for both chewing and sucking. 

 Ovipositor of the female may be modified into a sting, piercing 

 organ or saw. Complete metamorphosis. 



Examples: A pis mellifica, honeybee; Bombus pennsylvanicus, 

 a bumblebee; Vespa maculata, a social wasp, builds large papier- 

 mache nests; Trypoxylon albitarsis, mud-dauber wasp; Vespa 

 maculifrons, yellow jacket; Monomorium pharaonis, red ant, 

 common about houses ; Megarhyssa, a genus of ichneumon flies, 

 the females of which drill through the wood of trees to parasitize 

 wood-boring insect larvae; Cimbex americana, a sawfly. The 

 ovipositor of the female is composed of two sharp plates, the 

 saws, flanked on either side by saw guides and is used in depos- 

 iting the eggs in the bark of maples, elms, and other trees. 



PHYLUM 15— MOLLUSCA 



Molluscs are soft-bodied, bilaterally symmetrical, unsegmented 

 animals, with only a remnant of a coelom, and usually enclosed 

 in a shell. In well-developed molluscs, like the snail, four body 

 parts can be distinguished: (1) the visceral sac, containing the 

 viscera and forming the bulk of the body. This is continuous 

 in front with (2) the head, bearing the mouth, tentacles, and eyes. 

 (3) The foot, the organ of locomotion, lies ventral to the visceral 

 sac. (4) The pallium, or mantle, is a dermal fold, forming 

 between it and the sac a mantle cavity which is provided with 

 gills or lungs, and receives the openings of the intestine, reproduc- 

 tive ducts and excretory organs. The outer surface of the 

 mantle secretes the shell (Fig. 252). 



The nervous system, typically, consists of three pairs of ganglia 

 connected by cords: (1) The cerebral ganglia lie dorsal to the 

 esophagus and supply the sense organs of the head. (2) The 

 pedal ganglia lie in the foot, and supply statocysts and muscle. 

 (3) The visceral ganglia lie in the viscera, which they supply, and 

 also send nerves to the osphradia, organs of chemical sense 

 located in the mantle cavity. 



