STRUCTURE OF TAPE-WORMS. 111 
ers and two large median ventral hooks on the hinder end. 
The ripe eggs are deposited in the water in winter, when 
the ciliated young, with four eyes and without suckers, find 
their way into the gill-cavities of tadpoles, whence, during 
or after metamorphosis, they pass into the urinary bladder 
of young frogs; P. integerrimum Rudolphi lives in that. 
of Rana temporaria (Claus’ Zoologie). 
A case of budding or parthenogenesis is said to occur in 
the genus Gyrodactylus. This is a very small Trematode 
with a large terminal disk, bearing a peripheral set of pow- 
erful hooks, with two long curved median spines. The 
body of the hermaphrodite worm shelters a daughter, a 
granddaughter, and great-granddaughter generation. G. ele- 
gans Nordmann lives on the gills of Cyprinoid and other 
fresh-water fishes. Dactylogyrus lays eggs, not being par- 
thenogenetic ; it has four head-flaps. D. amphibothrium. 
Wagener lives on the gills of the stone-perch ; D. fallax 
Wagener on Cyprinus rutilus.. 
Order 3. Cestodes.—The common tape-worm is the type 
of this order. Specimens may be procured from physicians, 
and a careful examination of cross-sections and ordinary 
dissections will convince the student that the tape-worm has 
no mouth, although a head armed with suckers or hooks. 
The body is divided into an enormous number of segments 
or proglottids, but there is no digestive canal, the worm 
living immersed in the contents of the intestines of its host ; 
its food being absorbed from the juices of its host through 
the walls of the body. 
The tape-worms and their allies have recently been found 
by Dr. Lang to possess a nervous system. The water- 
vascular system is well developed in the Cestodes, where it. 
seems to be excretory in its functions, as in the Trematodes. 
There are usually four, sometimes only two, longitudinat 
canals, which are connected in the head and in each segment 
with transverse anastomosing branches, while from these main. 
canals a network of fine vessels branch out. Granules and 
whitish chalky deposits occur in the canals, and these con- 
cretions, like simflar bodies in the excretory canals of Tre- 
matodes, seem to have, Leuckart claims, a relation like that 
