CRUSTACEA. 



5* 



J of maxilke, which would indicate that the head-shield 

 is really made of five consolidated rings. It will be 

 noticed that the eyes are set in the head, and not 

 borne upon stalks. For this reason, the Gammarus 

 and the Idotaea are placed among the sessile-eyed 

 Crustacea. Kdriopthalmia. while the lobster belongs to 

 the stalk-eyed division of the class. Podopthalmia. 



l'OI" UTHAl.MIA. 



This general division of the class includes, among 

 the forms already described, Nebalia and a host of 

 similar animals, most of them represented by fossils, 

 the genera Lucifer. Squilla, and the like, of the order 

 Stomapoda, as well as the following groups belonging 

 to the order of the Decapoda. 



Anomoura. 



This group, in so far as its range of form and struc- 

 ture is concerned, is in reality equivalent 10 both 

 Macroura and Brachyura. The habits of the hermit- 

 crab (Figs. 22, 23) are very instructive to children. 

 The arms are used both for walking and getting food, 

 etc., the second and third pairs of thoraic limbs for 

 walking alone, and the fifth pair are crooked and 

 help to hold the animal in the shell, the fourth pair 

 being probably useful in this way also. The seg- 

 ment of the fifth pair is wholly free from the thorax, 

 and seems to belong to the abdomen, when viewed 

 from the dorsal side. The abdomen is soft and bag- 

 like. The first ring has no appendages; the second, 



