A. Diagrammatic figure showing method 

 used by drill in boring a hole in the shell of a 



trum; r, radula, which works backward and for- 

 ward over a pulley-like arrangement, and files 

 or rasps the hole. 



B. Piece of the shell of a quahog, showing 

 the round hole bored by the drill. 



bivalves, and the radula rasps a hole through the shell by a backward 

 and forward motion, the fine particles of lime filed away being swallowed 

 by the drill. It is said that when the bivalve becomes exhausted, it 

 opens its valves, and that the drill then enters by this opening, as do also 

 other mollusks and crabs which have been waiting for this opportunity." 



Feeling rather tired by our 

 walk across the muddy shore, we 

 sat down on the sandy beach 

 above high-water mark, and Pro- 

 fessor Parker gave us the follow- 

 ing account of the homes of 

 marine mollusks : 



" Naturalists have divided the 



Sea into Certain definite regions, clam - m, mouth; o, throat; p, proboscis, or ros- 



f~T~n m T* VQ r\ n 1 a rrrVi i r V n'^-flrci I-*O/-IJ'TTTO t*f-\ n - *-1 f*-v_ 



each characterized by a certain 

 kind of life. One of these divis- 

 ions varies according to latitude 

 (we speak of the fauna of the arctic regions, of the temperate regions, 

 and of the tropical regions), but the division which I desire to speak 

 about is that of depth. The older naturalists divided the shore regions 

 into the Laminarian zone, or region of brown kelp ; and the Coralline zone, 

 or region of stony algae. Later scientists, however, divide the regions 

 according to other characteristics. Thus, the region bordering the shore 

 which supports marine vegetation, and to which light can penetrate, is 

 called the Littoral region ; that of the deep sea, to which no light can 

 penetrate, is called the Abyssal or Benthal region ; and the region lying 

 between these two is called Archibenthal. The Littoral region may be 

 said to extend from the shore to a depth of one hundred fathoms, and 

 the conditions are here the most favorable for life, being supplied with 

 warm, fresh currents which afford the animals abundant food. 



u The Littoral region may also be divided into several subordinate 

 areas, characterized by the kind of life. The first is the Littoral region 

 proper, which includes that part of the beach lying between high and 

 low water. The next area is called the Laminarian zone, for the reason 

 that the long-leaved kelp, or Laminaria, lives chiefly in this region. It 

 extends from low-water mark to about fifteen fathoms in depth. The 

 third area is the Coralline zone, so called because the vegetation consists 

 principally of stony algae. Small coralline animals, or Polyzoa, are 

 abundant, and this region is generally supposed to extend to a depth of 

 one hundred fathoms. 



" Beyond the Littoral region the shore gradually slopes into deep water, 



87 



