392 



SGIEJSrCE. 



[Vol. VI., No. 143. 



of the main lines of the country. The capital is 

 forthcoming, and it is quite likely that in a few 

 years this mountain, which is of such great inter- 

 est in geologic, topographic, and artistic respects, 

 will have acquired an almost incalculable indus- 

 trial importance. 



NATURAL ENEMIES OF OYSTERS. 



Man in former times, and even at present in 

 some localities, might be classed with the enemies 

 of the oyster. But now, when he is inti'oducing 

 artificial means for their multiplication, instead of 

 an enemy he becomes their protector. There are 

 animals, harmless-looking and small, which do far 

 more damage to this delicious shell-fish than man, 

 and that, too, without giving anything in return. 

 The many which are destroyed by human agency 

 become few when compared to those killed by their 

 smaUer foes. 



The oyster, although protected by a very hard 

 shell that can be closed almost hermetically, is, on 

 the whole, rather poorly defended, for there he lies 

 right on the open bottom, exposed to everything 

 that may chance to come along, without any 

 power to move away and crawl into some crevice, 

 but destined to remain motionless while attacked. 

 Two kinds of animals do the most damage : one 

 the common star-fish (Asterias Forbesii), the other 

 a univalve spiral shell-fish, called by oystermenthe 

 ' driU ' (Eurosalpinx cinerea). 



A star-fish approaches its victim, slowly crawls 

 upon it, and then bends its five arms around the 

 shell. The mouth of a star fish is so small that an 

 oyster a quarter of an inch long could not be taken 

 into it. So what does it do, when its arms are en- 

 circled around the large oyster, but begin to pro- 

 ject its stomach out of its mouth and surround the 

 oyster with its stomach entirely outside of the 

 body. Then the oyster gradually opens its shell, 

 leaving the star-fish to do as it pleases. After a 

 while the star-fish moves off, and we see that a 

 large part of the oyster is gone. When the 

 stomach is first protruded a hquid is excreted 

 which seems to have the power of either killing 

 or weakening the oyster. Just as soon as the 

 shells are open digestion is begun by the star-fish, 

 and after a short time the hunger of the star-fish 

 is satisfied and the oyster is dead. Before long the 

 star-fish feels like another meal, and he attacks 

 another oyster, leaving the old one as prey to small 

 crabs and shrimp. And so it goes on day after day, 

 thousands operating in the same manner. At times 

 they come in immense swarms from deeper water, 

 in a single night entirely destroying a large bed. 

 In brackish water they do not flourish, but in the 

 almost pure ocean water found in some oyster- 



raising districts the destruction is immense, and 

 there is no remedy. 



If some shell-fish for which the star-fish have a 

 preference could be introduced among the oysters, 

 perhaps the devastation might be partially checked. 

 Oystermen formerly had the stupid habit of tearing 

 every star-fish that happened to come in their way 

 into pieces, throwing the fragments overboard. 

 They were not aware that each arm had the power 

 of reproducing the remaining four arms and be- 

 coming a perfect star, so that each time one was 

 torn into two or three pieces, two or three new 

 individuals were formed. 



The other enemy, the so-called ' drill,' is well 

 named, for its peculiar operations are based upon 

 its boring or drilling powers. Although seldom 

 an inch long, it can bore a hole through the hard 

 shell of an oyster with surprising speed. The hole 

 is always smooth and about in the same place, a 

 spot covering a vital part being the point attacked. 

 Similar ' di'ills ' operate on other species of shell- 

 fish, and their deadly marks can be seen on the 

 valves of the shells which are washed upon our 

 beaches. In any collection of shells, and on any 

 beach, numerous examples of the neatly-drilled 

 hole can be found. 



In the soft animal part of the ' drill ' there is a 

 little tube-like proboscis which encloses another 

 proboscis. Over the end of the latter there runs a 

 little ribbon which is covered with teeth. This 

 ribbon, or odontophore, is attached at each end on 

 the two opposite sides of the inner proboscis. By 

 means of muscles at the base of each end of the 

 ribbon it may be pulled back and forth over the 

 end of the snout, with the teeth projecting out- 

 ward. When the oyster is to be attacked, the end 

 of the snout is pressed against that part of the shell 

 to be bored, and the muscles begin to work the 

 toothed strap. The teeth rasp away at the shell, 

 each time removing particles of calcareous matter 

 until a hole is bored. Then the rasp acts upon the 

 flesh mside, and as the meat is removed it is drawn 

 to the mouth and eaten. 



The ' drill,' after eating a meal, leaves its vic- 

 tim, and later attacks another. By the time it has 

 finished its meal the oyster is dead, and its shell 

 flies open, leaving the rest to crabs and shrimp. 

 Filing away upon the hard shell wears the teeth 

 away rapidly, but this is remedied by nature, for 

 one end of the strap is gradually absorbed, while 

 from the other end a new supply of toothed ribbon 

 is being formed. So, on one side of the proboscis, 

 there are fresh unused teeth ; on the other side, old 

 worn ones ; and on the end, teeth just being worn ; 

 and the whole gradually moving away to one end, 

 to be absorbed while other fresh ones are being 

 formed. Ralph S. Tarr. 



