LEUCKART, ON DEVELOPMENT OF ECHINORHYNCBUS. 65 
proboscis-cavity. They are developed from a special layer of 
cells which originate in the subcuticular granular layer, and 
which is especially related to the inner tunic of the head. Before 
the hooklets, which first make their appearance, are fully 
formed, the formation of the rest begins, so that the entire 
proboscis is soon completely armed. But as soon as this 
armature is completed the proboscis is retracted, the retrac- 
tion commencing by the introversion at first of the vertex 
into the neck, and afterwards when the introversion by the 
continued growth of the body extends beyond this part, into 
the proper cavity of the body. Thus it is only at a later 
period that that peculiar conformation is assumed which has 
been so often remarked in the Echinorhynchi, frequently met 
with in an encysted condition in the flesh and intestines of 
fish, and what has been compared with the conditions pre- 
sented in the Cysticerci. The form of the Echinorhynchi is 
at first rather slender, and almost fusiform. It would seem to 
require some time to assume the rounded shape. 
When the introversion of the neck begins will be observed 
for the first time the commencement of the so-termed 
‘‘lemnisci,” which are at first short and contracted. With 
respect to the origin and relations of these organs to the peri- 
pheral vascular system, I am at present unable to make any 
positive statement. Nor have I as yet investigated the 
changes undergone by these entozoa after they have reached 
the intestine of their ultimate host; but this investigation 
shall be undertaken on the first opportunity. Considering 
the relatively high development of the young parasites, these 
changes, it may be presumed, will be found to be but simple, 
and probably passed through in the course of a few days, 
whilst the metamorphosis of the embryo, up to the formation 
of the Echinorhynchus, occupies, on the whole, about six 
weeks. 
Tn conclusion, I would, moreover, remark that the parasitism 
of the young Echinorhynchi is not unfrequently fatal to their 
entertainer. This is particularly the case in those instances 
in which the parasites are numerous—in some I have seen 
fifty or sixty,—and in the later stages of their development. 
In the young state, these entozoa, notwithstanding the free- 
dom with which they exert their boring powers, are but little 
injurious. 
Giessen ; Aug. 28th, 1862. 
VOL. IIT.—NEW SER. E 
