MACALISTER, ON ASCARIS DACTYLURIS, 85 
and bordered by a slightly prominent lip or margin. The 
coats of the duct thicken, and the cavity contracts imme- 
diately before it ends at this aperture. When some of these 
females were left immersed in water for a week the ova 
commenced to become developed. At first the eggs were 
filled with the finely granular, irregularly divided vitellus, 
which regularly segmented. Its first stages of segmentation 
escaped my observation, and many ova presented six, nine, or 
more globules of the parted yolk when first I examined them. 
Soon the mass became finely granular, and assumed an ellip- 
tical shape, which in some became curved or arcuated. The 
two extremities then begin to be differentiated, and from the 
posterior end a lateral turn or projection extends, at first 
short, but soon considerably elongating, until it becomes re- 
markably like the tail of the adult, twisted to one side. The 
anterior end becomes blunt and somewhat flattened, and no 
granules appear in it. At this stage, in some of the more 
perfect, a moniliform thread appears to pass down the centre 
of the body from the mouth to the root of the tail SG ese 
forming the primitive trace of the alimentary canal. 
I was not able to observe the development of the ee 
tory apparatus, but it is probable that it does not appear until 
the young animal has become liberated from its shell. All 
the changes which I have noted took place inside the oviduct 
of the mother, but I also observed ova floating in the sur- 
rounding fluid in similar conditions of development. 
The male sexual organs are made up of, first, a testis, 
tubular and elongated, but not as long as the ovary; this 
begins small and rapidly thickens, until it rivals the intestine 
in size; this is at first filled with an indistinct granular 
material, but afterwards contains more perfectly elaborated 
spermatic fluid. These tubes are not easily unravelled, and 
in some males (probably those which are immature) the whole 
glandular mass seems as though it were a lobulated indivisible 
structure. _ Near the posterior extremity of the body the 
testicular tube ends in a large dark, rough, bilobed, seminal 
vesicle, which lies on the ventral surface of the intestine, and 
sends off below a narrow duct to the root of the intromittent 
organ. In front of the blunt bevelled tail projects the 
spiculum, a slightly curved body with a pointed pen-shaped 
extremity ; half of it is included in a canal in the animal’s 
body, from which it passes by a small opening, whose pro- 
jecting margins overlay its sides for a short distance. 
A little im front, and to the side of the large spiculum, 
a smaller one is seen, much more acute, and communicating 
with the spermatic vesicle by a small canal. This second 
