THE SILKWORM A MPHITRITE. 
243 
tremity of the body, however, is very small and slender, and is 
doubled back upon itself, with its tip pointing to the mouth of 
the tube. 
The structure of the tube is extremely variable. Some indi- 
viduals seem to give all their endeavours towards making their 
dwelling as long and strong as possible, while others are content 
with a tube which is barely long enough to shelter the whole 
body. They work with great rapidity, and when confined in an 
aquarium, will build their sandy homes nearly as well as if they 
were at liberty in the sea. Many interesting experiments have 
been made upon their modes of working, and by a judicious 
supply of different substances, they may be forced to build 
tubes of various colours and forms. 
There is another group of tube-making marine annelids 
which are remarkable for the transparency of their newly con- 
structed dwellings. Of these a very singular example is found 
in the Silkworm Amphitrite (. Amphitrite bombyx). 
The reader will remember that one, at least, of the Terebeilae 
can make a structure which is as transparent as isinglass, and 
will not, therefore, be surprised to find that another annelid 
possesses similar powers. The tube of the Silkworm Amphi- 
trite is longer than the body, and is made entirely of the gela- 
tinous secretion which in most of the species is used as a 
cement for fastening together the sand, shells, mud, and other 
materials of which the tube is formed.. In this creature, how- 
ever, the secretion is so plentiful, that it forms the whole of the 
tube. 
Nor does it content itself with a single tube, but forms several, 
one after the other. When first made, the tube is so beautifully 
transparent, that the body of the inhabitant can be seen almost 
as plainly as through glass; but in process of time, it becomes 
incrusted with mud and sand, and almost looks as if it were 
made ol very dirty leather. The average length of an adult 
specimen is three inches, and its beautiful gill-fan is decorated 
with brown and yellow. As is the case with most of the tube- 
inhabiting worms, it is a very timid creature, jerking itself into 
