6S 
this point of its life being yet imperfectly known. From this egg¬ 
like larva proceeds the second larva form which is known as a Redia. 
Its mode of development in this form is not fully known. It is now 
found attached usually to the body of some water snail ( Paludina ), 
the cilia of the first larva having now disappeared. When the Redia 
or this second larva form has acquired its complete growth it is some¬ 
what of an arrowhead shape; consisting of a sac, within which is sus¬ 
pended a tubular bag containing colored masses, which Huxley sup¬ 
poses are alimentary. The head is represented by a kind of crown, 
and near the other extremity are two lateral projections. In the body 
cavity external to the tabular sac vesicles now appear which rapidly 
increase and assume the form of cercarice , the name given to the 
third larval stage. The Heclia now bursts and these new zooids es¬ 
cape. This multiplication at an intermediate and incomplete stage, 
before sexual characters have appeared, is very remarkable and intro¬ 
duces to our view a strange feature in animal life. 
The Cercaria resembles a peanut with a slender tail attached to 
one end; it also has lateral membranous attachments by means of 
which it swims after the manner of a tad-pole. After swimming free 
for a certain length of time it finally fixes itself upon and usually 
bores its way into the body of a water snail or some similar mollusk. 
The tail then drops off and the body encloses itself in a cyst. The 
coronal hooklets of the perfect form now appear. It now remains 
quiescent unable to develope further in its present situation; awaiting 
for some water-bird to swallow the mollu-k in which it is imbedded. 
As soon as this is done, and the cyst set free in the alimentry canal 
of the bird further development begins and the complete or Distoma 
form is assumed. The body elongates and narrows anteriorly, the 
suckers move nearer the head and the circle of hooklets being com¬ 
plete, it attaches itself by these to the walls of the intestine. 
Such is the strange life history of this intestinal worm; and although 
that of the liver-fluke may vary in some respects yet it is doubtless 
similar in a general sense. 
The following outline given in my address before the Illinois Wool- 
Growers’ Association, September 20, 1877, is probably substantially cor¬ 
rect: 
They produce a kind *of spore or egg; but its subsequent progress, 
so far as it is at present known, presents one of those singular life- 
histories occasionally met with in the lower orders of animals. In some 
way, not well understood, this egg or germ spore makes its way to the 
external world; its history from this time until it is hatched is un¬ 
known; but moisture in some form is probably necessary to its devel¬ 
opment. It is next found in the body of some mollusk, as the snail, 
or some aquatic insect, where its for n is so different from that of its 
after life, that it was long considered as appertaining to an entirely 
different group of animals. From these, in some way not yet ascer¬ 
tained, it passes into the sheep. It probably escapes from the mol¬ 
lusk or insect to herbage in moist places, or water, and is taken into 
the stomach of the sheep with its food or drink, and passes through 
the lacteals, and makes way to the ducts of the liver. 
As sheep do not feed on mollusks, as the water-birds do. it is diffi¬ 
cult to imagine how the Cercaria if it becomes encysted in the body 
of the mullosk, makes its way into the stomach of the sheep. It is 
possible this may be explained in one of two ways: First, as has 
