XERILLA AN ARCH I AX X EL ID . 
415 
has been shown to occur in Saccocirrus, Dinophilus, and 
Histriobdella. But it is one of the points I have not yet been 
able to determine for certain. Never have I seen spermatozoa 
in a living female ; but in one series of sections o£ a female 
which has shed its large ova, nnmerous spermatozoa are 
present in the ovisacs. 
An account ot‘ the maturation of the germ-cells and of the 
embryology is reserved for a future paper. The eggs are 
laid in groups, each being enclosed in a transparent shell. 
Development is direct; there being no free-swimming larva 
the young are hatched as little worms. 
The Morphology op the Genital Ducts. 
The absence of nephridia in the genital segments m ighfc 
lead one to conclude that nephridia have been directly con- 
verted into genital ducts in these segments ; but this is 
almost certainly not the case. Much more probable is it that 
the ducts are nephromixia, or mere coelomostomes (6, 7). In 
Protodrilus, Pierantoni has described large-funnelled organs 
in the sexually mature worm, which have all the appearance 
of nephromixia ( 14 ). These ducts closely resemble the 
nephromixia of the Syllids, formed at maturity by the graft- 
ing on to the nephridial funnel of a large funnel derived 
from the coelomic epithelium (7). Somewhat similar tubes 
are found in Saccocirrus (8), which, at all events in the male, 
are probably of the same compound nature. More difficult 
to interpret is the case of Polygordius. Here the genital 
products escape by breaking through the body-wall, and the 
coelomostomes have consequently degenerated. The nepli- 
ridium of the larva is closed and provided with solenocytes 
(7, 9), and the nephridium of the adult opens by a true neph- 
rostome (see my fig. 46, PI. 42, 7). If coelomostomes are 
developed at all, it can only be at the time of maturity, and to a 
small extent. Funnels, apparently of coelomic origin, have 
indeed been described by Fraipont ( 5 ) and Hempelmann ( 12 ;. 
On the other hand it is very doubtful whether the nephridia 
