458 Proceedings of the Royal Society 
in minute structure * between the two portions of tbe copulatory 
pouch. In Lumbricus complanatus there is no difference in shape ; 
only a difference in size, and the structure is identical. This matter 
is a little more important than might appear at first sight, because if 
we are to allow that the two large pouches in segment nine are each 
the equivalent of a copulatory pouch, we shall have the apparent 
anomaly of two pairs of copulatory pouches in the same segment. 
It is generally believed that the segment which contains the 
gizzard is in reality the equivalent of two segments which have 
become fused through the abortion of the intervening septum, 
possibly of mechanical advantage to the gizzard, as rendering its 
movements more free. In Perichceta affinis , Perrer records! the 
presence of two pairs of copulatory pouches in the gizzard “ segment,” 
besides two rings of set®. I have observed the same thing in other 
species of this genus. Is it legitimate to suppose that in L. com- 
planatus we have a record of the former presence of the gizzard in 
the same region of the body where it now occurs in Perichceta , 
though not in any Lumbricus ? 
The supposition of an aborted mesentery and a consequent fusion of 
two segments is not, however, so trustworthy in this species as in 
Perichceta, because there is certainly only one nephridium and one row 
of setae as in all the adjacent segments, and so, perhaps, it is better 
to suppose that the copulatory pouch of segment 8 has a very large 
diverticulum, — larger than the pouch itself, — a more normal arrange- 
ment being found on the left side of the body. A third alternative 
is possible, viz., that more than a single pair of copulatory pouches 
may be present in the same segment. As an evident abnormality, I 
have observed a case of this kind in a specimen of Perichceta affinis — 
the species which has already been referred to above as affording 
an instance of variability in the number of the copulatory pouches 
in different individuals of the same species ; in one specimen of this 
worm there were three copulatory pouches in one segment placed in 
a row. An inspection of fig. 2 would appear at first sight to prove 
that the second alternative mentioned above is the correct one. In 
every case it will be noticed that the duct of the pouch passes 
backwards to open on to the exterior at a point opposite the 
* Proc. Zool. Soc., 1885, p. 829. 
+ Nouv. Arch. d. Mus., t. viii. p. 111. 
