50 HYDROPIC DEGENERATION. 



fitting animals and become developed into agamozooids. If any- 

 thing is to come of these wanderings, however that is to say, if 

 the cestoid embryos are to propagate, two main conditions must 

 be fulfilled. In the first placg, the localities chosen for lodge- 

 ment must afford suitable nourishment; in the second place, 

 the animal selected by the embryo as its home must afford an 

 opportunity to the scolex developed within it, to reach the 

 appointed intestinal canal of a vertebrate animal, either by active 

 or passive emigration, in order to accomplish its sexual development 

 and propagation. That the cestoid embryos should often go far 

 astray in their wanderings, whereby these conditions are left unful- 

 filled, is easily conceivable ; however, these strayed cestoid embryos 

 do not perish, but notwithstanding the degeneration which they un- 

 dergo retain sufficient tenacity of life to be capable of further 

 development and propagation. Objections have been raised by 

 some to the opinion I have just expressed, that strayed cestoid 

 agamozooids may undergo dropsical degeneration; audit is urged, 

 on the contrary, that the vesicles of these hydropic scolices are a 

 necessary organ, a sort of reservoir of nutriment. In answer to 

 this, I can only repeat what I have already said in another place, 1 

 in vindication of my views, viz., that I cannot see why one should 

 deny the possibility of a degeneration in form among worms, 

 since it is observed in the higher animals, where the modifi- 

 cations produced by climatic influences and change of food are at 

 once admitted as " Races." If, in many of these races, an extra- 

 ordinarily luxuriant growth of hair shoots out over the whole 

 body, or on various parts of it ; if the horns of certain races of 

 ruminants have the property of lengthening, or even of doubling ; 

 if the ears of certain kinds of our domesticated animals become 

 disproportionately long and drooping; if, in some races, local 

 fatty degeneration takes place in the shape of a fatty tail or 

 hump, why should not an accumulation of serous fluid in certain 

 parts of the body, giving rise to a local dropsy, take place 

 amongst the lower orders of animals, when these are exposed to 

 the influences of an unusual mode of life ? 



The processes of degeneration to which the cestoid embryos 

 are liable in their wanderings are of two different kinds ; either 

 the body of an embryo lengthens posteriorly into a solid caudal 

 appendage, or else it becomes distended into a watery vesicle by 



1 ' Zeitschrift fur Wiss. Zoologie,' Bd. iv, 1853, p. 407. 



