I897-] Friknd. — The T^ibe-Forming Worms. 295 



Lumbriciis, so the worm which made a tube was naturally 

 Lumbricus tubifex. In time the various worms came to be 

 distinguished not only as species, but as genera ; then the old 

 specific term tubifex became generic. For a long time, just 

 as every earthworm came to be known as Lumbricus terrestris, 

 so all the blood-worms found in ditch and stream, pond or 

 river, were denominated Tubifex rivulorum. Eventually it 

 appeared that there were many forms of Tubifex, and that they 

 diflfered so widely the one from the other that they must be 

 separated into different genera under the family name of 

 TubificidcB. Now this family is both large and interesting. 

 Its members are found in many parts of the world, and 

 numerous students of the front rank in this branch of zoology 

 have during the last twenty years given them attention. 

 Foremost among these I may mention our English authorities 

 Beddard and Benham. In America we have the infatigable 

 Swedish worker Bisen. Vejdovsky, Stole, and others are the 

 Continental representatives. By their combined labours 

 nearly twenty different genera have been discovered and des- 

 cribed, and it would require a considerable volume to reproduce 

 all that is now known on the subject. 



The family is distinguished from most others by certain 

 well-defined characteristics, while in some particulars the 

 affinities with the other families are equally clear. Thus the 

 genus Ilyodrilus, which is unmistakeably tubificid in 

 character, is in many respects closely allied to the Nai- 

 domorpha (Beddard, " Monograph of Oligochaeta," p. 227) 

 These connecting links are of the greatest value in relation to 

 the question of evolution. 



Speaking generally, the members of this family may be dis- 

 tinguished by their delicate and slender build ; their trans- 

 parent integument, through which the blood-vessels and 

 vital organs may as a rule be readily distinguished ; and 

 especially by the shape, number and variety of their setae. 

 These vary greatly. In one or two genera the setae are of 

 one kind only : in others there are two different kinds, while 

 yet other genera have three and even four different forms. 

 Sometimes one kind is uniformly distributed over the whole 

 body, at other times one kind occurs on the dorsal, and 

 another on the ventral, or one on the anterior, and another on 



