130 Macueay Memortat Vouume. 
between these transverse lobes of the vitelline gland, separating them from one 
another with some degree of regularity. In 7. Sempert, T. /heringi and certain of 
the others this disposition, in accordance with the absence of the rudimentary septa, 
is not observable—the arrangement being quite irregular. On either side there is 
given off behind a thin-walled duct which runs inwards and backwards and eventually 
opens with its fellow into the oviduct close to the ovary and receptaculum vitelli. 
As regards the minute structure: the lobes consist of large irregular cells with 
a tendency to a radial arrangement round the axis of the lobe. The protoplasm of 
the cells contains large granules. Frequently spaces appear between the adjacent 
cells, sometimes uniting to form a central cavity: these are irregular and are 
apparently formed by the breaking down of portions of the cells to form the 
secretion, the particles of which find their way, apparently, through these irregular 
spaces to reach the duct. 
XIV.— Repropuction. 
Self-impregnation is quite possible in Zemnocephala. The cirrus is capable of 
being protruded far enough to penetrate into the uterus. The elaborate arrangement 
of spines which, inverted when the cirrus is at rest, bristle outwards from the end of 
the organ when it is protruded, obviously subserve copulation; but their great 
development in some of the species would seem rather to indicate cross- than self- 
fertilisation, since in the latter process they would not appear to be necessary. Telling 
still more strongly in favour of the view that cross-fertilisation takes place, is the 
presence in 7. NMove-zealandie of the remarkably powerful muscular vagina with its 
formidable array of teeth already described—a structure which can only have been 
developed with a view to retaining the cirrus of another individual until the 
spermatozoa had been discharged. In two instances I have found on examining 
series of sections of 7. Dendyz that the specimen had been killed with the penis 
protruded through the genital aperture.* The preponderance of evidence would thus 
seem to be in favour of the occurrence of cross-fertilisation. 
During the period of sexual activity large quantities of spermatozoa are developed 
in the testes, and are constantly passing along the vasa deferentia. They accumulate 
in the sperm-sac, which they greatly distend, and in the interior of which they 
circulate with slow streaming movements. A few at a time pass into the ejaculatory 
sac, where they become very active. The contraction of the ejaculatory sac is always 
followed by the protrusion, to a greater or less extent, of the cirrus, accompanied 
* One of these is figured in fig. 7 of Plate xm. It may, however, have been in the act of being used as a weapon, 
