315 
which, up to the present time, has generally been described 
as always existing in the species. This consists in a pair of 
pyriform organs, which are placed together in the eleventh 
segment of the creature. Each is enclosed within a special 
membrane. The ova are arranged from above downwards, 
on one side of each ovary, in such a manner that the largest, 
that is, the ripest, are placed at the lower part, whilst the less 
mature ascend one above the other as far as the apex of each 
organ. The regular gradation in the size of the ova gives to 
the ovaries a characteristic appearance. The ripe ova are 
discharged through a rupture in the enclosing membrane. 
Besides this, stated by Ratzel to be the principal form, 
another condition has been found in which the ovaries 
resemble those existing in Enchytrseus. This state of things 
has during a course of observations on 150 specimens of 
Tubifex been found in one out of every twelve. The ovaries 
are placed in the eleventh segment, on each side of the 
intestine, like those in the Tubifex, but are here broken up 
into a number of globular masses averaging in size from 
0 6 to 0 8 min., which lie side by side in the general cavity 
of the body, and are not contained within any special mem- 
brane. These masses, which float about the general cavity, 
are really groups of ova, and each generally contains one 
large and ripe ovum. As this is the normal form of ovary 
in Enchytrseus, Ratzel applies to a similar construction in 
occasional specimens of Tubifex the name of the second, or 
Enchytrseus form. In endeavouring to account for the remark- 
able phenomenon of the occasional appearance in tubifex of a 
form of ovary found constantly in another species, Ratzel can- 
not accept the view that it is owing to some pathological change. 
To this are opposed the facts of the perfectly normal condi- 
tion of the rest of the organization in such cases, the perfect 
resemblance of all the ovaries thus formed, and the number 
of individuals found with these organs in this condition. 
Ratzel did not find a single instance of the Enchytrseus 
form of ovary in an examination of over a hundred speci- 
mens of Limnodrilus, a w orm closely allied to Tubifex. He 
is inclined to look upon this phenomenon as an instance of 
atavism and reversion in structure, and believes that though 
Tubifex and Enchytrseus stand far apart in the group of the 
Oligochseta, the species are yet so closely allied as to render 
reversion a possible occurrence. 
Cysttcercus Lumbriculi. Dr. Fritz Ratzel, Arckiv fur 
Naturgeschichte, heft 2, 1868. — According to Dr. Ratzel 
many specimens of Lumbriculus variegatus have been found 
infested at all seasons of the year by a parasitic creature, 
VOL. IX. NEW SER. X 
