Estory of the Nematode Worms. 453 
The seminal elements have retained their early cellular form 
in the upper extremity of the testis. Posteriorly these cells in- 
crease, with simultaneous formation of granules, to balls of fully 
0:02 millim., which break up by quadripartition, and then form 
the genuine seminal corpuscles (of 0°005 millim.) not unfre- 
quently met with after copulation, even in the interior of the 
female organ among the ova. 
After impregnation the eggs continually increase in size (up 
to 0:08 millim. in length and 0:04 millim. in thickness) ; and at 
the same time commences the ordinary segmentation, which 
soon (in summer sometimes on the third day) leads to the sepa- 
ration of a long and slender embryo of disproportionate size 
(0°25 millim. m length). The number of these embryos of 
course depends upon that of the mature ova; and this, as already 
remarked, is 1 summer nearly twice as great as in winter. 
However, it is not only the ova (even the immature ones) that 
increase in size after impregnation, but also the female animals, 
which in the gravid condition (although only in summer) grow 
to a length of 1 millim. 
Originally, of course, the embryos lie within the genital tube, 
enclosed in a thin egg-membrane. But the latter is lost as soon 
as the rolled-up embryo begins to extend itself. The delicate 
wall of the genital tube also can only resist the movements of 
the embryo for a short time. Soon atter their development the 
young are seen free in the body-cavity of the mother, the wall 
of the genital tube beg destroyed, and the mass of eggs scat- 
tered through the whole body. 
This destruction of the genital tube is, however, only the 
introduction to a further breaking-up, which does not continue 
confined to the ova, but soon attacks the chyle-intestine, and 
finally even the pharynx and the muscular mass of the body. 
All these structures break up, under the constant lively move- 
ments of the embryos, into a finely granular detritus. In four 
or five days after the commencement of the experiments (at least 
in summer, for in winter this period is extended to ten or twelve 
days) there remains nothing of the original worm except the 
external chitinous envelope, with the embryos, whose undulatory 
movements are so strong that, at the first glance, the mother 
might be supposed to be still alive. 
As long as the embryos remain in the body of their mother 
they are, as regards the structure of the pharynx, regular Rhab- 
ditides, with two dilatations, and teeth in the posterior bulb. 
But hardly have they escaped from their surrounding membrane 
than both the teeth and the dilatations are lost. The pharynx 
then forms a slender cylinder, with a slight thickening at the 
hinder extremity. The animals are also remarkably different 
