182 BIOLOGY FOR BEGINNERS 



most of which are adapted for different purposes (being developed 

 from the ordinary swimming leg) as is shown in the tabulation. 

 The front of the carapace extends forward into a protective beak, 

 the rostrum (why so called?) , on either side of which are the eyes, 

 set on movable stalks and each composed of many lenses. 



Head Appendages. Beginning at the anterior (head) end, we 

 first come to the small and large feelers (antennae) at whose base 

 open the ear sacs and excretory organs respectively. Then come 

 the true jaws (mandibles) and two pairs of little jaws (maxillae) 

 which aid in chewing the food. To the posterior maxilla is attached 

 the " gill bailer," a scoop-shaped organ for paddling water over 

 the gills, the flow being toward the anterior. So far, the organs 

 named belong to the head. Notice the various functions performed. 

 Also observe that the jaws work from side to side and not up and 

 down, because they are merely leg-like appendages adapted for 

 chewing and so continue to have a horizontal motion as do the legs. 



Thoracic Appendages. The first appendages of the thorax are 

 three pairs of maxillipeds (jaw feet) whose function is holding and 

 chewing food. To these are attached gills for respiration. Next 

 come the large claws, evidently for defence and food getting, then 

 two pairs of legs with claws at the tip and two more pairs with- 

 out claws. These four pairs of legs are concerned mainly with 

 walking, and to them and to the large claws as well, gills are at- 

 tached, which extend up under the carapace into the gill chamber. 



Abdominal Appendages. The appendages of the abdomen are 

 called swimmerets and are similar on the first five segments, being 

 adapted for paddling forward in the water. They are also used by 

 the female for attachment of her eggs. The sixth swimmeret is 

 enormously developed into a wide fin or flipper while the ap- 

 pendage of the seventh segment is reduced to a mere spine and the 

 segment itself is flattened. The' sixth and seventh segments to- 

 gether form a powerful organ for backward locomotion, for they can 

 be whipped forward by the strong muscles of the abdomen and the 

 animal will shoot backward at high speed. 



Adaptation. While we do not have to memorize all these append- 

 ages, there are two lessons that their study must teach; first how 



