ORDER Il. THE SHELL-LESS ACEPHALES. 243 
landing-places, and destroy their foundations, gradually causing _ their 
destruction. 
They have an agreeable taste, and in some countries are much used for 
food. 
Trrepo. — The Teredines. This genus is celebrated for its power of 
destruction. By means of its small rhomboidal valves it excavates wood 
with great rapidity. It is not much over six inches in length, but in tropical 
countries there are species of a larger size. “Its shells, which are only a 
few lines broad, are very small compared with the size of the vermiform 
body, and are, therefore, completely inadequate for its defence. For better 
security, it bores deep passages in submerged timber, which it lines with a 
calcareous secretion, closing the opening with two small lids. Untortu- 
nately, while thus taking care of itself, it causes considerable damage to 
the works of man. It is principally to guard against the attacks of this 
worm that ships are sheathed with copper, and the beams of submarine 
constructions closely studded with nails. During the last century, the 
Teredo caused such devastations in the dikes which guard a great part 
of Holland against the encroachments of an overwhelming ocean, that the 
Dutch began to tremble for their safety ; and thus a miserable worm struck 
terror in the hearts of a nation which had Jaughed to scorn the tyranny 
of Philip II., and bade defiance to the legions of the no less infamous 
Louis XIV.” 
But while blaming the Teredo for its damages, justice bids us not pass 
over in silence the services which it renders to man. If it here and there 
destroys useful constructions, on the other hand, it removes the wrecks 
that would otherwise obstruct the entrance of rivers and harbors; and we 
may ask whether these services do not outweigh the harm it causes. 
ORDER II. THE SHELL-LESS ACEPHALES. 
This is a small order, divided into two families. The first family — 
Segregata —embraces those genera whose individuals are isolated, and 
without mutual organic connection, although they often live in societies. 
The most remarkable genus of this family is ; 
Satpa. —The Salpas “have the cloak and its cartilaginous envelope oval 
or cylindrical, and open at the two extremities. On the side of the anus 
the aperture is transverse, wide, and furnished with a valve, which allows 
the water to enter, but prevents its egress; on the side of the mouth the 
aperture is simply tubular. Muscular bands embrace the cloak and con- 
tract the body. The animal moyes by forcing out from the anterior aperture 
