THE BIONOMICS OF ENGLISH OLIGOCHiETA 13 



groups of worms are adapted, from the standpoint of their 

 blood constituents, to different modes of life. The answer to 

 the question, What is the role of the Pachydrilids or red- 

 blooded Enchytraeids, therefore, is to be discovered by experi- 

 ment and a careful study of their life-history. We proceed, 

 therefore, to a summary of the principal investigations which 

 have been carried out in this connection up till the present 

 time. 



A Brief Historical Survey. — As already stated, the term 

 Pachydrilus was first employed by Claparede in 1861, in which 

 year he published what may be regarded as a pioneer study in 

 this group of annelids. Although his work appeared in French, 

 it had reference to our British Isles. Having spent some time 

 in the investigation of the worms found on the seashore in the 

 Hebrides, he gave the results in the Memoires de la Societe de 

 Physique et d'Histoire naturelle de Geneve (vol. 16, i. 75 seq.). 



Later research, it is true, showed that the eminent Danish 

 zoologist, O. F. Miiller (6) so long ago as 1771, or nearly a 

 century before the time of Claparede, had described some species 

 of Pachydrilus under such names as Gordius, Lumbricus, or 

 Nais. But each of these terms has in the course of time been 

 allocated to other families or genera, and all are to-day in 

 systematic use. But in 1843-4 Oersted (8) employed the 

 term Lumbricillus, and of recent years this name has been 

 given precedence over Claparede's Pachydrilus. It is still, 

 however, convenient to speak of the red-blooded forms as 

 Pachydrilids, since, though there are two genera in the group, 

 they are so closely related that they can only be differentiated 

 by the structure of one of the sexual organs after they have 

 reached the adult stage. The distinction is minute, but it 

 serves to break up a large number of species into smaller sections 

 which are easier to handle than the larger and more unwieldy 

 genera. 



The Earliest Known Species. — Perhaps the first species to 

 become the subject of diagnosis was Lumbricillus lineatus 

 O. F. Miiller, which was described in 1771 as" Gordius pallidus 

 linea longitudinale rufa," and was three years later named 

 by the author (7) Lumbricus lineatus. This worm has been 

 frequently studied, but in spite of all the attention bestowed 

 upon it and its allies, we are unable even to-day to define it 

 with such exactitude as to ensure its being readily and un- 



