Mistory of the Nematode Worms. 339 
shaped chitinous tube, separates at the circumference of the latter 
from the adherent parenchyma and gradually retracts itself more 
and more. The cavity which is thus produced in front of the 
cesophagus has at first, of course, the form of a meniscus; and it 
retams this as long as the funnel-shaped chitinous tube which 
unites the cesophagus with the buccal orifice persists ; but when 
the latter breaks up on the approach of the next change of skin 
and the cesophagus sinks in posteriorly, the cavity becomes deeper 
and more globular in its form. Its inner surface then becomes 
clothed with a chitinous lamella, which, on the walls of the buccal 
orifice, passes over continuously into the new cuticle formed 
beneath the old one, and, after the casting of the latter, speedily 
acquires a yellowish brown colour. This covering is, however, 
quite distinct from the future buccal cup; it is not only smaller 
but also furnished with a different sculpture. ven after its 
second change of skin our worm is certainly not yet the definitive 
Cucullanus. It is much smaller (at the utmost 0°8 millim.) and 
has no sexual differentiation. The sexual organs, scarcely larger 
than in the embryo, consist of a simple bean-shaped body, which 
is attached to the ventral wallimmediately in front of the middle 
of the chyle-intestine. On the abbreviated caudal extremity 
the worms bear three small points, which subsequently (after the — 
sexual differentiation) are found only im the female individuals. 
In summer I have sometimes observed the stages of develop- 
ment here described within six days after the infection of the Cy- 
clopes, while in winter three weeks not unfrequently elapse before 
they are completed. To all appearance, however, the parasitism of 
these animals is very fatal to their host; almost all the infected 
Cyclopes are observed to die soon after the ¢ompletion of the 
developmental processes above described. At the same time it 
must be borne in mind that, in the small aquaria of the ex- 
perimenter, the parasites penetrate into their hosts in far greater 
numbers than would ever be the case in the open water. 
The last phase of development is only passed through in the 
interior of the final host. The young Cucullani, in the form of 
small asexual worms with a simply sculptured buccal cup, are taken 
up by the perch with its food (the Cyclopes), when they grow 
rapidly and at the next change of skin cast off their previous 
larval characters; at the same time the sexual differentiation 
takes place, carrying the animals quickly towards their perfect 
maturity. Within ten days or a fortnight after their transfer 
into the intestines of the perch, the young Cucullani must have 
already effected their copulation. 
When we glance over the life-history of the Cucullanus as here 
brietly described, we again find in it essentially (and still more 
completely than in the Trichine and Ollulani) the same picture 
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