^22 OUGOCHAETA 



neighbourhood of genital segments. Blood yellow or red, dorsal vessel arises 



behind clitellum and is without cardiac body. No salivary glands. Testes 



multiple ; sperm-duct long. Copulatory glands often present. 



The genus Pachydrilus was instituted by Clapaeede, but not defined in such 



a way as to distinguish it from Snchytraeus j in a subsequently published memoir 



he indicated the differences between Pachydrilus and Enchytraeus, whose near 



relationship he had not formerly appreciated. These differences are in the red 



blood of Pachydrilus, its living upon the sea-shore, and finally the absence of 



dorsal pores. 



Vaillant adopted this definition of the genus, with the exception of the marine 

 habit ; in his recent work upon the Oligochaeta he still adheres to it, modifying 

 the definitions so as not to be universally applicable. With the exception of Ana- 

 chaeta and Distichopus all the Enchytraeidae are referred to one of the two genera, 

 Pachydrilus and Enchytraeus. 



CLAPAEi;DE's distinctions were criticised by Eisen (13), who remarked that Pachydrilus lacteus 

 had colourless blood, and that all the red-blooded species do not live in water. Eisen therefore 

 re-united the two genera, and divided the genus thus formed into a number of subgenera on the 

 strength of the characters afforded by the shape of the brain. Michaelsen has criticised 

 Eisen's position, pointing out that the features used by CLAPARiiDE were not the sole points of 

 distinction between the genus Pachydrilus and its allies. Eisen's criticisms were to some extent 

 justified by reason of the fact that Clapak^ide placed in his genus Pachydrilus the species P. lacteus, 

 which has white blood. This species has also, as Michaelsen reminded us, setae unlike those of 

 other Pachydrilus in being straight, and therefore like those of the genus Enchytraeus; the fact 

 that it has, like other species of Pachydrilus, no dorsal pores is not a reason for including it in 



that genus, for in many species of Enchytraeus these pores are wanting. 



• 



The genus Pachydrilus was for the first time satisfactorily defined in Vejdovsky's 

 ' Monograph of the Enchytraeidae ' (p. 50) ; his definition is as follows : — ' Borsten 

 stark hakenformig gebogen. Blut ockergelb oder roth. Porus cephalicus zwisehen 

 dem Kopf- und Mundlappen in der Mittellinie des Riickens. Die Segmentalorgane 

 in alien Segmenten vorhanden, vom dritten anfangend. Hoden in biischelformigen 

 Gruppen, gestielt.' This definition, it wiU be seen, includes all the important points 

 mentioned ia Michaelsen's definition, but, as a matter of fact, Vejdovsky applied 

 it inaccurately when he included ^Pachydrilus' sphagnetoru/m ; this species, as was 

 afterwards shown by Michaelsen, has not lobed testes (Vejdovsky's specimens were 

 immature), and has, therefore, been relegated by Michaelsen to another, but very 

 nearly-i'elated genus Marionia. 



Michaelsen has argued that Deago's genus Epitdphusa is no more than 

 a Pachydrilus; it has red blood, and the testes are '^ bouquet,' two facts which 



