MARINE WORMS 173 



one preceding and following it. Though many of the worms are 

 generally looked upon as uninteresting creatures, of such an 

 unattractive appearance and with such depraved habits that they 

 are beneath respect, yet a study of the sub-kingdom will prove 

 that not only does it include a number of wonderful forms with 

 the most marvellous life histories, but that some of them are very 

 beautiful objects ; and this last remark refers more particularly to 

 many of the marine worms, which come directly within the scope 

 of our work. 



Before passing on to the special study and classification of the 

 marine species, however, we must say a few words concerning the 

 worms in general, reminding the reader that all our statements 

 regarding the anatomy of the creatures may be readily verified by 

 simple dissections of one or two typical species, such as the common 

 earthworm, the fisherman's lugworm, the sea mouse, or the 

 common horse-leech of our fresh-water ponds. With this object 

 in view, the animal may be killed by immersion in spirit, then 

 pinned out in the dissecting tray under water, and the body-wall 

 opened by means of a pair of sharp-pointed scissors. 



The digestive tube of a worm runs completely through the 

 length of the body, and though there is no distinct head, there is 

 always a mouth, and this is often provided with horny jaws, and 

 sometimes also with horny teeth, with which the animal is enabled 

 to inflict wounds on its prey. 



Like the preceding sub-kingdom the Echinodermata worms 

 possess a system of water tubes ; this system, however, is not in 

 any way connected with the function of locomotion, but is, in many 

 cases at least, if not in all, intimately associated with the process of 

 respiration. It consists of a series of tubes, arranged in pairs in the 

 successive segments, communicating with the body-cavity internally, 

 and opening at the exterior by means of pores in the cuticle. In 

 some there is a highly organised system of bloodvessels, con- 

 taining blood that is usually either colourless, red, or green, but 

 the colour of the blood is never due to the presence of corpuscles, 

 as is the case with higher animals, the tint being due to the 

 plasma or fluid portion of the blood ; and though worms cannot be 

 said to possess a true heart, yet they often have one or more con- 

 tractile bloodvessels which serve the purpose of propelling the blood. 



Most worms possess a nervous system, and, where this is 

 present, it consists of a chain of ganglia, placed along the ventral 

 side of the body, beneath the digestive tube, all united by means 



