PHYSIOLOGICAL SIGNIFICANCE OF THE CYST. 369 



striking since we can give no plausible explanation of it. It might 

 certainly be supposed that the watery contents of the bladder formed 

 a nutritive fluid, if this idea were not excluded by the extremely 

 small quantity of nutritive material which it contains (0'2 to 0'3 per 

 cent, of albuminoids, 1 and 0'03 to 0*05 of fat). Neither does the 

 chemical analysis of the water of the bladder show it to be an ex- 

 cretory product ; for it yields, apart from the above substances, a weak 

 saline solution (with about 3 per cent, of salts, mostly of soda). 



Under these circumstances, there is hardly any alternative but to 

 regard the collection of water as an arrangement for securing certain 

 individual advantages. Perhaps in this way a more favourable, that 

 is to say an increased, absorptive surface is furnished to the parasite, 

 or perhaps greater protective needs are thus met. A fact possibly 

 of importance in this last respect is that the genuine bladder- worms 

 are apparently exclusively confined to the Mammalia, so that some 

 protective arrangement is therefore very necessary to them, on 

 account of the size and motions of their hosts. The theory that the 

 effects secured by the apparent dropsy are of a mechanical nature, 

 seems the more plausible since similar arrangements have occasionally 

 been observed to fulfil similar functions in the Graffian follicles, in 

 the amnion, and in the eye. 



But when we use the term "bladder -worm" in a wider sense 

 than the older Helminthologists did, we note at once that the presence 

 of this developmental phase is by no means limited to the Tcenice, but 

 occurs on the whole almost universally among the Cestodes. One has 

 only to cast a glance over the often-quoted treatises of van Beneden 

 and Wagener to notice large numbers of such forms in the most 

 diverse families of tape-worms. Even Eudolphi observed this struc- 

 ture in a few of these bladder- worms. The forms which he mentions 

 belong exclusively to the marine group of the Tetrarhynchi, and, from 

 their size and occurrence in the muscles and in the parenchymatous 

 viscera (in fishes), must be allied to the genuine Cysticerci. These 

 worms could not of course be ranked with the genus Cysticercus, for 

 the form of their heads was quite different (" caput bothriis 2 vel 4 et 

 proboscidibus uncinatis 4 instructum"). They were therefore regarded 

 as the representatives of a distinct genus, Anthocephalus, which, by 

 the structure and armature of its head, recalled certain Bothriocephali 

 living in the intestines of rays and sharks (now called Tetrarhynchi, 

 Eudolphi's RliyncJiobothrii), just as the other bladder-worms recall 

 the Tcenice. 2 



1 It is on account of this small qxiantity of albumen that the bladder-fluid can be 

 coagulated neither by boiling nor by the addition of acids. 



3 Nitzsch in Ersch and Gruber's " Encyclop.," Art. Anthocephalus, Bd. iv., p. 259, 1820. 



2 A 



