$ 112. THE HELMINTHES. 117 
CHAPTER VII. 
RESPIRATORY SYSTEM. 
§ 112. 
A respiratory system has not yet been found with certainty in the 
Helminthes, i 
The pedunculated vesicles of many Nematodes, situated under the skin, 
and projecting into the cavity of the body, and which have great absorp- 
tive power, have been compared to trachean pouches and branchiae; but 
their structure is so little known, that any opinion as to their function 
ought to be deferred.” 
A remarkable fact is the presence in some Trematodes of extremely 
active vibratile lobules, situated intermittingly on the inner surface of the 
walls of the vessels.” It may be questioned if these vessels have a special 
function, different from that of the others. They somewhat resemble the 
aquiferous system of the Polyps, Acalephs, and Hchinoderms, and like it, 
belong, perhaps, to the respiratory system. They differ, however, in not 
having openings which communicate outwardly ; but, probably, they receive 
by endosmosis, water absorbed by the skin.® But another objection to this 
view, is, that in this order there has been found nothing like blood-vessels. 
belonging to the nutritive vessels. The nutritive 
liquid of the vascular system differs from the 
coarsely-granulated excretion of the excretory 
organ, by its homogeneous and colorless aspect. 
It is remarkable that in Distomum tereticolle 
this liquid has a reddish color, which, in the finest 
capillaries has a yellowish cast ; see Wiegmann’s 
Arch. 1835, I. p. 59. ; ‘ 
H. Meckel, likewise, thinks that the above-de- 
scribed vascular system of the Trematodes, is in 
direct communication with the secreting organ 
peculiar to these Helminthes ; see Muller’s Arch. 
1846, p. 2, Taf. I. fig. 2.* 
1 Bojanus (Isis, 1821, p. 187, Taf. ITI. fig. 51- 
5) affirms to have observed in Ascaris lumbri- 
coides these pedunculated vesicles, which are 
found also in Ascaris depressa, and Strongylus 
gigas, in connection with the lateral swellings ; 
but this throws no light upon the nature of these 
vesicles, for we are yet ignorant of that of these 
swellings. The stigmata which he affirms (loc. cit. 
p. 187, Taf. IIL. fig. 56) to have observed upon 
these lines with Ascaris acus, are, according to 
my own observations, only subcutaneous cell-like 
bodies. 
2T have quite distinctly seen these vessels with 
Diplozoon paradozum, Aspidogaster conchi- 
cola, Distomwm echinatum, and an allied species 
of this last from the intestine of Falco apivorus. 
*[§ 111, note 2.] Van Beneden (Ann. d. Se. 
Nat. 1852, XVIII. p: 23) has recentiy expressed 
doubts upon the presence of a circulatory system 
I am yet uncertain if the vibratile organs found 
in the neck of Distomum globiporum and nodu- 
losum (Wiegmann’s Arch. 1836, I. p. 218), and 
in the parenchyma of Distomum duplicatum be- 
hind the ventral sucker, are of the same nature. 
Ehrenberg (Wiegmann’s Arch. 1835, II. p. 
128) was the first who observed this ciliary move- 
ment in the vessels of Diplozoon. When the 
motions of these lobules are free, there is a rapid 
current of the liquid, as Nordmann has remarked 
(Microgr. Beitr. Hft. I. p. 69). But if an animal 
is compressed between two plates of glass, and 
their motions thus impeded, it will be quickly seen 
that these last are the cause of the circulation ; in 
fact, when the lobules cease moving, the colorless, 
homogeneous, and, without doubt circulatory liquid, 
is no longer perceived. 
3 Burmeister (Handbuch d. Naturgesch. 1837, 
p. 528) compares, not without reason, this system 
to the trachean system of insects, the first being 
aqueous, and the second aerial respiratory organs, 
thus confounding this vascular system of Helmin- 
thes with the excretory organ and duct found in 
most Trematodes, There may be, however, a com- 
parison between these two systems, if we except 
the insects with stigmata, and take those which are’ 
aquatic and have a pletely closed trach 
apparatus (see below), admitting no air from with- 
out. 
the Cestodes and Trematodes, but see the 
| piates of Blanchard, Ann. d. Sc. Nat. 
1848, X. Pl. XI. — Ep. 
with 
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