ON THE NEMATODES OF THE COMMON EAETHWORM. 623 
Jeptoderian form^ described by Biitscbli, but wrongdy regarded 
by him as belonging’ to the same species, by the name Rhab- 
ditis pellio Biitschli, non Schneider. No doubt the correct 
course would be to call the “ leptoderian ” species by a new 
name, but until Schneider’s “peloderian” species has been 
re-examined, I hesitate to take this logical step. 
In reading this paper no confusion should, I think, be 
caused by this splitting of what has hitherto been regarded 
as one species. This paper deals exclusively with Biitschli’s 
leptoderian” form,whichI callRliabditis pellio Biitschli, 
non Schneider, the species whose larvm, both free and encysted, 
infest the living worm, and it is this form which is intended 
when the abbreviation Rh. pellio B. is used. 
Anatomy. 
It will be well at this point to say something of the anatomy 
of Rliabditis pellio B. since the descriptions given by 
Schneider, Biitschli and von Linstow are not quite complete. 
'I'he accompanying table of measurements is intended to 
show the inferiority in size of the adult I’eared on peptone to 
tlie typical form fed on decaying worm. 'I’he arrangement is 
based on the admirable system used by Maupas (15). The 
fractions express the relation between the length of the 
particular region and the total length of the body. The 
length given for the buccal cavity, however, is relative to the 
total length of the oesophagus, of which it is regarded as part. 
'I'he measurements of the adults — subject as they are to great 
variation — have been taken as far as possible Irom thelai-gest 
individuals obtained. 
The cuticle is transparent, and marked by exceedingly . 
delicate ti-ansverse striations difficult to distinguish except at 
tlie anterior and posterior ends. 
’I'he mouth (PI. 37, fig. 6) is bordered by three lips, one 
dorsal and two ventral, each of which is divided by a shallow 
groove into two lobes. Each lobe bears a pair of fine short 
papillae. The buccal cavity in side view appears to be cylin- 
