ANATOMY OF THE EARTHWORM. 17 
with the modification. This is the view advanced by .M. 
Claparéde, and universally received, with regard to the 
Limiculous oligochetes. What may be the relations between 
the segment organs of the Terricole and their efferent ducts, 
is the question which now occurs. M. Claparéde, at the 
conclusion of his ‘ Recherches,’ briefly refers to this question, 
merely to mention its difficulty, and to promise a future 
attempt to answer it. 
In every segment of the earthworm but the first we have 
a normal segment organ opening near the median ventral 
line, and in the 10th, 11th, 14th, and 15th rings we have the 
apertures placed more laterally (always beyond the first series 
of sete) of the sperm reservoirs, the efferent canals, and the 
oviducts,—organs presenting marked and decisive points of 
similarity in structure to the normal segment organs, and 
also to the corresponding modified segment organs in the 
Limicole. Are not, then, the efferent ducts and sperm 
reservoirs of the earthworm modified segment organs? It 
is hardly possible to deny the probability of this, in 
the face of the similarities of structure and general 
homologies existing between the Limicole and Terri- 
cole, which would be totally upset were we to conceive that 
the reproductive ducts of each are constructed upon entirely 
different plans. Assuming, then, that the efferent ducts of 
Luwbricus and its spermatic reservoirs are modified segment 
organs, and the actual homologues of the segment organs are 
ducts of the Limicole, we can only account for the presence 
of two segment organs ina single segment—a normal and a 
modified one—by conceiving the typical number of segment 
organs in the oligochetee generally to be four in each segment, 
a pair on either side, one or both of which may be suppressed. 
or modified (see Pl. I, fig. 5) ; as also we have four setigerous 
glands, of which one pair may be suppressed. In the Limi- 
cole both pairs of segment organs are suppressed im the first 
six segments, and a single pair throughout the rest of the 
body. In the Terricolz, on the contrary, both pairs are absent 
only in the first anterior segment, whilst one pair is sup- 
pressed throughout all the other segments excepting those very 
vascular and well-nourished segments containing the “ geni- 
talia,” with which the second pair of segment organs here 
unsuppressed, is connected. This view of the case is further 
borne out by the presence of a double pair of what may be con- 
sidered as modified segment organs, in each segment of the 
leech and perhaps some other Annelids. Seeing that the ovary 
or the testis, from the protozoon, with its nucleus and nucleolus, 
up to man himself, are homologous structures in each group o 
VOL. V.--NEW SER. B 
