THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 83 
next disappear and the ovum rounds off and appears more or less in the middle of 
the ovary as a mature ovum. The form and structure of the mature ovum is 
exceedingly characteristic. There is a large nucleus, which has lost its granular 
_ appearance and assumed a transparent, vesicular aspect, and in the protoplasm 
around it there are always several large food granules (perhaps better called 
oil-globules by Moseley). Moseley (6) describes the mature ovum in Bipalium as 
invested by a distinct external capsule derived from the stroma of the ovary. Such a 
capsule does not occur in my sections of Geoplana. Possibly, however, it may be 
represented by the spindle-shaped cells seen at an earlier stage of development. It is, 
however, curious, if so, that these should subsequently disappear, and it appears to me 
not improbable that they may be nutrient cells from which the ovum derives its very 
abundant supply of food particles or oil-globules. Moseley does not describe these 
nutrient cells, but it is not impossible that he has overlooked them, and the capsule 
observed by him in the adult ovam may be derived from their remains. Altogether 
the ovary of Geoplana agrees very closely in structure with that of Bipalium. 
The mode in which the oviduct opens into the ovary is remarkable. A very 
evident papilla projects into the cavity of the ovary on its outer side and a little behind 
the middle of its length (Fig. 42). At the apex of this papilla is the opening of the 
oviduct. 
(6) The Oviducts.—The oviduct, on reaching the base of the papilla on which its 
intra-ovarian opening is placed, first of all makes a sharp and very short turn dorsally, 
and then runs straight towards the posterior end of the animal, keeping, for almost its 
entire length, close along the top of the longitudinal nerve cord, where it is always 
to be found in transverse sections (Fig. 4, od.) 
In Geoplana traversti also, according to Moseley (1), the oviduct leaves the ovary 
on its outer side, and the same is true of Bipaliwm; while in Rhynchodenus it leaves 
the ovary on the inner side. 
Moseley has fully described the histological structure of the oviduct in the two 
latter genera, and in Geoplana spenceri we find exactly the same structure, viz., a thin 
basement membrane supporting a layer of distinctly nucleated columnar cells, with 
strongly developed cilia projecting into the lumen of the duct (Fig. 34). 
At brief intervals along its course, branches are given off from the dorsal aspect 
of the oviduct, which run upwards for a short distance (Fig. 34). These, as I shall 
presently show, lead to the yolk glands. Moseley (6) describes similar branches in 
Bipalium, but states that in Rhynchodemus they are absent. He regards them as the 
rudiments of the branched ovary possessed by lower Planarians. Von Kennel (3) 
found them to exist also in Rhynchodemus terrestris. 
