HISTOLOGY OF THE LAND-PLAN ARI AN S OF CEYLON. 
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arrangement exists in the case of the testes. The ovary was filled, in all the specimens 
which I examined, with ova in all stages of development, the riper ova occupying the 
central and lower regions of its cavity, and the less mature the peripheral. 
A meshwork of connective-tissue fibres with spindle-cells upon them passes from the 
walls of the ovary between the ova, and apparently furnishes the capsules in which the 
mature ova are seen to be contained. This meshwork is best seen in Rhynchodemus 
(Plate XIII. fig. 13). The successive stages in the development of the ova are given in 
Plate XIII. fig. 12. In its earliest stage the ovum is indistinguishable from the cellular 
lining of the sac of the ovary : it then apparently becomes rounded and increases in 
size, the germinal vesicle as well as the surrounding yelk remaining finely granulated 
up to a certain stage ; then the germinal vesicle clears up and becomes transparent, 
and the ovum becomes enclosed in a capsule with a transparent area between it and the 
capsular wall. The final stage consists in the development of transparent fatty looking 
vesicles or globules within the fine granulated yelk-area. I am uncertain whether the 
capsules here described as enclosing the ova in their latest stages descend with them 
into the uterus, or whether they are merely ovarian follicles which open in the ovary 
and allow of the escape of the ripe ova. From a study of the ovary of Rhynchodemus , 
in which these capsules are not so well marked, and when present more apparently con- 
nected with the stroma of the ovary, I was led to consider that such was probably the 
case. If it be so, then it is quite possible that several ova may subsequently be enclosed 
within one true egg-capsule formed in the uterus, as in JDendrocoelum lacteum. At the 
base of the cavity occupied by the ovary of Bijpalium is a mass of small rounded spindle- 
cells, which may represent an accessory gland in a rudimentary condition. In one 
specimen of Bipalium which I examined there was present on each side, just externally 
to the lower extremities of the ovaries, a small mass of large nucleated cells (Plate XIII. 
fig. 8, g ) connected by a pedicle with the ovary itself. This mass, though extremely 
well defined in this one specimen, was absent entirely in many others, and present only 
as a trace in some few. It may represent a yelk-gland in a rudimentary condition, or 
possibly, as all specimens which I obtained had their testes and ovaries filled with ova 
and spermatozoa, this accessory gland had already performed its function for the season 
in the formation of ova, and had shrunk in consequence. The former hypothesis is, 
however, most probably correct, since the female organs generally in Bijyalium seem to 
be undergoing a process of simplification. No corresponding glandular mass was seen 
in Rhynchodemus. The oviduct leaves the ovary on its outer side in Bi'palium , on its 
inner in Rhynchodemus. The duct consists in both animals of an external well-marked 
basement membrane, on which rest internally a series of well-defined nucleated cells, 
which are rectangular in longitudinal section, truncated cuneiform in transverse section. 
These cells bear long hairs or cilia, which are inclined in a direction from the ovary 
towards the uterus, and in transverse sections of the oviduct show a spiral twist (Plate 
XIII. fig. 9). The hairs are in many parts of the oviduct so long that it seems possible 
that they have no vibrating motion, but more probably act merely so as to prevent the 
MDCCCLXXIV. T 
