"THINGS IINRECK'D OP." 165 



sand with only the siphonal orifices exposed to 

 the light, perceives the slightest shadow falling 

 upon the water. This has led to closer study 

 of the siphonal margins where what seem tiny 

 eye specks have been detected. 



" We are told that some of our shellfishes 

 are supplied with auditorial nerves, while an 

 external ear is credited to some. Yet their 

 whole external surface is so extremely sensitive, 

 aside from the especially sensitive tentacula, 

 that they perceive the approach of any object 

 by vibration ; hence naturalists tell us we need 

 not expect a very strongly developed sense of 

 sound. 



" Your last question I can best answer by 

 reading you what some wise students have 

 written concerning these interesting little crea- 

 tures. ' If you ask what can be the use of ears 

 to a class of animals which are invariably dumb, 

 I answer though this is true vdth respect to 

 the great majority, yet it may be only that our 

 senses are too dull to perceive the delicate 

 sounds which they utter, and which may be 

 sufficiently audible to their more sensitive or- 

 gans ; and, besides, some moUusca can certainly 

 emit sounds audible to us. Two very elegant 

 species of sea-slug — viz., ^oUs punctata and 

 Tritonia arborescens (now called Dend^'onotus 



