THE CRUSTACEA 115 



Very often the visitor to the shore may, when sitting 

 quietly on a rock, have noticed a peculiar little rasping 

 noise, very difficult to locate. This is caused by the 

 myriads of little valves of the acorn-barnacles rubbing 

 against the firmly fixed portion of the shell, as the little 

 inmate, perhaps anxious for a turn of the tide, moves 

 uneasily within its home. 



If a piece of stone or a shell bearing a few specimens is 

 placed in a bottle of sea-water, and looked at against the 

 light, the beautiful little " feather feet " will be seen to 

 protrude and begin their operation. 



An idea of how abundant these barnacles are can be seen 

 by glancing at the rocks in Fig. 93, just below the octopus. 

 Myriads of the Nauplius and Cypris stages of these occur 

 on the surface of the sea during the summer months, and 

 very frequently a muslin net drawn through the water 

 will be lined with the cast skins of the feather feet, these 

 retaining the beautiful structure of joints and bristles in 

 perfection. 



There are several species on our shores. The common 

 one is Balanus balanoides. 



Fig. 46 shows a number that are attached to the back of 

 a crab, and their " feather feet " can be seen extruded. 



There are many other representatives of the Cirripedia, 

 but we shall just glance at one more. It is such as to 

 upset all our ideas of what constitutes " resemblance." 

 This is Sacculina carcini. It is a Cirripede " of every 

 grace, of every virtue shorn." One that by the habit of 

 parasitism and the disuse of parts has degenerated into 

 little more than a sack. 



It has no feet nor shell, simply a membraneous bag 

 about the size of a hazel nut, and a series of threads like 

 an unravelled bit of string. 



It attaches itself when in the Cypris stage to the end of 

 the alimentary canal of a crab, where it remains through 



