18 ANATOMY OF THE EARTHWORM. 
the animal kingdom, being specialised developments, and not 
modifications of existing structures, the homologies of the 
reproductive organs of the earthworm may be considered as 
satisfactorily ascertained, the testes and ovaries being the 
homologues of testis and ovary in all other animals, and the 
efferent canals and sperm reservoirs the homologues of the 
system of ciliated canals or segment organs common to. most 
Annelida, and remarkable in the group of oligochetes as 
, being developed into auxiliary organs of reproduction. r 
In PIII, fig. J, an ideal typical segment of an oligochete 
is drawn. Suppress the pair of canals attached nearest the 
ventral surface, and the type of the Limicolous group is 
obtained. Conceive the exterior pair converted each into a 
blind sac, and the type of the segment containing the sperm 
reservoirs in Lumbricus is seen. Imagine three such tubes 
as the exterior, blended; and the bifurcated ciliated vas 
deferens of Lumbricns results, whilst both are suppressed 
altogether, to form the anterior segments of the Limicole, or 
left almost without modification to form the fourteenth 
segment of the earthworm, with its oviducts and segment 
organs. 
‘Recapitulation. —The generative organs of the earthworm 
consist of two pairs of testes, Sanaa” in the eleventh and 
twelfth segments, connected with two seminal vesicles; a 
pair of bifurcated ciliated vasa deferentia, connected with 
each testis by means of a ciliated re ceptacle enveloped in 
the fibrous sheath of the testis, and opening in the fifteenth 
segment; a pair of minute transparent ovaries situated 
in the thirteenth segment, opposite the orifices, of two ovi- 
ducts placed in the fourteenth; a pair of spermatic reservoirs 
in the tenth and eleventh segments: five pairs of capsulo-genous 
glands, andtaecingulum. The sperm reservoirs, the oviducts, 
and vasa deferentia, are homologous with the same organs of 
the Limicolz (Natide), and are the modifications of a series 
of segment organs suppressed in other annuli. The normal 
seyment organs exist in all segments but the first two, and 
form an inner series which is suppressed in the Limicole, 
whose segment orgaas are the representatives of the exterior 
series suppressed in all but six segments of the Terricole. 
All the segment organs, however, should be considered as 
homologous. 
(Lo be continued.) 
* In the Limicole it appears to be the interior series of segment organs, 
or those which form the normal ciliated tubes in the Terricole, which are 
suppressed. 
