Introduciio7i to Animal Morphology. 339 



Sense-organs are well developed in the higher 

 Crustacea. The antennae are organs of touch, and 

 possess, near their points, groups of minute rod-like 

 ner\'e-endings like short stiffbristles, into which nerves 

 pass, and end in a granular protoplasm. Similar, 

 but more elongated, bodies in the anterior antenna 

 are supposed to be olfactory, or else a conical organ (in 

 Decapods) at the base of the outer antenna, whose free 

 end is either open or closed, maybe an organ of smell. 

 The olfactory rods are better developed in males 

 than in females, and are sometimes pectinated. 



The ear is a dermal sac, either closed, containing 

 an otolith, or open, with a simple or complex mouth, 

 sometimes containing a foreign body acting as an 

 otolith. The cavity is lined with regularly disposed, 

 stiff acoustic hairs^ either attached to the otolith, and 

 holding it in its place, or free at one end. These hairs 

 have their shafts continuous with a delicate, superfi- 

 cial, chitinous layer lining the vesicle, and are only con- 

 nected to the deeper structures by their axes. Similar 

 hairs, like the sensory rods of the antenna, are found 

 out of the vesicle. 



The organ in Decapods is open at the base of the inner 

 Fig. 38. 





Crangonyx subterraneus, a blind Crustacean. 



antennule, and supplied by a branch of the inner antennary 



Z 2 



