LAMP SHELLS. 45 



one, attracting the attention of many a fish to the dainty 

 morsel seemingly outlined in fire. 



Giglioli refers to the luminosity of an undescribed Hetero- 

 pod, the axis of whose body gave out a reddish light when- 

 ever the animal was excited. According to C. W. Peach, 

 the young of Uolis are phosphorescent. Such instances where 

 the animal is particularly defenceless are amusing refuta- 

 tions of the theories of naturalists who see in the light a 

 warning. 



The common garden slugs, the cousins of the snails, are 

 well-known forms. They generally remain concealed during 

 the day, coming out at night, and often doing much damage 

 to vegetation which is largely laid to birds. I have kept many 

 of them, and they offered an extremely interesting study. 

 They secrete a remarkable amount of mucus, which they 

 use in descending from a tree, just as a spider does its silk 

 thread. The mucus exudes from the foot, passes along to 

 the tail, when it is attached to the twig. This accomplished, 

 the slug boldly launches itself into space, the thread becom- 

 ing more and more attenuated, until finally, when the slug 

 is near the ground, it is exceedingly fine. Nearly all our 

 common slugs descend from trees in this manner, — quite a 

 contrast to the slow, tedious ascent. 



The amount of mucus that can be taken from them is 

 remarkable ; and that it is also protective will be evident to 

 any one who may experiment with them. 



One genus, Phosphorax, found at Cape Verde, and, accord- 

 ing to Duncan, at Teneriffe, has a luminous pore on the 

 posterior border of the mantle. One species only is known, 

 P. noctilucus ; and its light has not, that I am aware, been 

 made the object of any extended investigation. 



