322 MR. R. OWEN’S DESCRIPTION OF A MICROSCOPIC ENTOZOON 
part : it appears to be a layer only of the external cyst, which, as is often seen in cysts 
of corresponding structure not formed by Hydatids', is more or less detached from the 
outer layer. 
In almost every instance in which I have succeeded in opening the cyst without 
injury to the worm within, it has been expelled entire, together with the fluid matter 
surrounding it, by pressure upon the cyst. Occasionally, however, a part of the worm 
remains adherent ; but this has been accompanied with a glairy adhesive state of the fluid 
secretion of the cyst, and has been, I believe, dependent upon it ; for when the broken 
pieces have been extracted and examined with a high power, both extremities have 
presented the same entire surface and uniform rounded appearance as in the worms 
which are extracted whole. 
The structure and relations of the cyst, therefore, and the absence of all organical 
connexion between it and the contained worm, lead to the conclusion that the cyst is 
adventitious, foreign to the Entozoon, and composed of the cellular substance of the 
body infested, morbidly altered by the irritation of the worm. 
From the tenacity of irritability manifested by the Trichina under circumstances so 
opposite to those under which it was developed, from its small size compared with the 
cavity of the cyst, and from the quantity of fluid in which it is immersed, it is highly 
probable that in its natural condition it enjoys active powers of motion. If in such 
movements the extremities of the worm were repeatedly pressed against the surrounding 
capsule, this would yield and become elongated in the directions where there was least 
resistance ; viz. where the muscular fasciculi would most readily separate, and obser- 
vation shows that it is in the direction of the fasciculi that the cysts are elongated. 
If the germ of a Trichina, or a portion of the worm separated by spontaneous fission, 
be deposited at the end of one of the elongated axes of the cyst, it might in the process 
of development excite the adhesive inflammation, which would then cut off the commu- 
nication between the smaller cyst and that of the parent worm, while the former would 
be stimulated to secrete from its inner surface a serous fluid, and so go on enlarging in 
size, through the influence of the same causes as occasioned the formation of the cyst of 
the parent. Smaller cysts of different sizes are occasionally seen thus attached to one 
end of larger cysts, and I am inclined to account in this manner for their formation. 
Cysts filled with opake matter are also occasionally seen. In these the worm may 
have perished, or its germ, after exciting the cyst to secrete, may not have been deve- 
loped, and the enlargement of the cyst may be occasioned by the accumulation of its 
own secretion. But these appearances are not sufficient to establish the independent 
vitality or existence of the cyst, in opposition to those analogies which so plainly point 
out its true nature and origin. 
' This separation of cysts alternating with a secretion of fluid is the cause of the Pill-bor Hydatid of 
Mr. Hunter, which is not a distinct animal or true Entozoon. 
