~ 
522 FRANK E. BEDDARD. 
§ Homology between Genital Ducts and Nephridia 
in the Oligocheta. 
The homology between genital ducts and nephridia has 
been a question of interest in Annelid morphology for some 
years. But the evidence in favour of the homology, as 
regards the Oligocheta, has hitherto rested upon comparatively 
few facts; indeed, some of the arguments that have been used 
were based upon inaccurate observation. Claparéde pointed 
to the absence of nephridia in the genital segments of the 
aquatic genera as evidence that the genital ducts were the 
slightly altered nephridia. Vejdovsky, however, discovered 
that the nephridia are at first present in the genital segments 
of these worms, but that on the maturation of the genital 
products and the development of special efferent ducts they 
disappear. Some years ago Lankester (20) put forward the 
ingenious suggestion that in earthworms (Lumbricus was 
at that time the only type known anatomically) the genital 
ducts represented the sole remaining traces of a set of ventral 
nephridia corresponding to the persistent dorsal nephridia. 
This view subsequently received a good deal of support from the 
researches of Perrier into the anatomy of earthworms. Perrier 
discovered that in some genera the dorsal set of nephridia 
were retained while the apertures of the genital organs were 
related to the ventral sete, showing, therefore, an interesting 
reversal of the conditions in Lumbricus. Later (6) Perrier 
found that in Plutellus the nephridia actually alternated 
from segment to segment, which of course was a further con- 
firmation of the view that originally two pairs of nephridia 
existed in each segment of the body in earthworms. Mr. 
Benham’s discovery (4) of a form—Brachydrilus—actually 
possessing two pairs of nephridia in each segment would have 
clinched the matter had it been made a little earlier, but 
would at the same time have necessitated some alteration in 
the hypothesis as formulated by Lankester, for in Brachy- 
drilus the genital segments also contain two pairs of 
