THE SILKWORM AMPHITRITE. 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 Terebellae 

 can make a structure which is as transparent as isinglass, and 

 will not, therefore, be surprised to find that another annehd 

 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 of very dirty leather. The average length of an adult 

 specimen is three incheis, 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 



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