ox THE NEMATODES OF THE COMMON EARTHWORM. 627 
There is a great deal of vai-iation ia the disposition of tlie 
bursal papillse in different individuals, even of the same brood. 
Single papillae may be missing’, extra ones may be present, or 
the usual intervals between papillae may be altered. These 
variations may occur on one side of the bursa only, or on both. 
The fifth papilla may be nearer the fourth than the sixth, or 
the intervals between the fourth, fifth and sixth, or between 
the seventh, eighth and ninth may all be equal. 
The papillae do not reach the edge of the bursa but bend 
round, their ends pointing perpendicularly away fi’om its 
ventral surface. The copulatory spicules (PI. 37, fig. 9) are 
strong, slightly curved and thickened at their anterior ends. 
They are structui’ally independent of each other but work in 
unison. The accessory piece (PI. 37, fig. lOj is a little moi’e 
than half the length of the spicules. The testis (PI. 37, fig. 1) 
is full of spermatozoa in different stages of development. The 
vas deferens is a tube formed of large cells with small nuclei. 
The lumen is narrow. The spermatozoa are oval and granular 
with a refractive nucleus of irregular outline. 
Quf!sTioNS OF Sex. 
(1) Analysis and Character of Reproduction. 
The work of Maupas (14), supplemented by that of Potts 
(15), has shown that in Rhabditis and several closely related 
genera the mode of reproduction is by no means uniform. At 
first it was thought that all species were bisexual. It is now 
known that side by side with the bisexual species, in which 
males and females are produced in equal numbers, herma- 
phrodite and parthenogenetic species also exist. 
In the hermaphrodite species, which appear to be even 
more numerous than the bisexual species, the females repro- 
duce as self-fertilising protandrous hermaphrodites and 
constitute the bulk of the individuals, as a rule vastly 
outnumbering the males, which in some species are almost 
entirely wanting. The males, though apparently as perfectly 
