+128 THE HELMINTHES. § 118. 
The few observations hitherto made upon thé genital organs of the Gor- 
diacei have shown that they are wholly tubular as in the Nematodes. But 
their intimate structure, and the development of their spermatic particles 
are so strikingly different, that this point alone would justify their separ- 
ation from the Nematodes, 
§ 118. 
With the exception of the Nematodes, and Gordiacei, the development of 
all Helminthes, which reproduce by means of genital organs and eggs, is 
metamorphotic. A complete series, from beginning to end of these meta- 
morphoses has yet never been observed with any species. From the separate 
parts of it here and there which have been observed, there appears the. 
remarkable fact, that the embryos after escaping the egg, are not always 
changed at the end of the metamorphosis, into individuals like the parent, but 
appear as larva-like animals, capable in their turn of producing other larvae. 
These last larvae alone, chatige into individuals, which are like the parent. 
This particular kind of transformation and development which is quite 
common among the Trematodes, has received the name of Alternate Gene- 
ration.” Whether it occurs among the Cestodes and Acanthocephali, 
cannot now be stated positively, for as yet we are unacquainted with the 
first period of their metamorphosis, — the embryo as it escapes from the- 
egg. In many Cestodes and Trematodes, the embryos are developed 
before the eggs are cast, and in some of the last order, they make their 
escape while the eggs are in the uterus. 
The development of the Cestodes occurs as follows: After the disap- 
pearance of the germinative vesicle, large, transparent embryonic cells. 
appear in the midst of the vitellus, which undergoes fissuration. 
These 
multiply by: division, increasing at the expense of the vitellus, which in the 
tightly to the vulva of the female in this act, that 
they cannot disengage themselves (Siebold and 
Nathusius, in Wiegmann’s Arch. 1836, I. p. 105, 
Taf. III. 1837, I. p. 60, 66). With many other 
species of Strongylus, and Ascaris, it is not rare 
to find a brownish gum about the vulva, and in 
which there is, sometimes, the very distinct impress 
of the male caudal valve (Mehdis, Isis,1831, p. 87).* 
10In the genus Mermis formed by Dujardin, 
the tubular uterus, the muscular vagina, and the 
vulva situated far from the caudal extremity, — all 
remind one much of the Nematodes. The eggs of 
Mermis nigrescens, like those of Ascaris den- 
tata, have long fibrillated appendages (Dujardin 
Ann. d. Sc. Nat. 1842, XVILI. p. 183, PI. VI., and 
Siebold, in Wiegmann’s Arch. 1843, II. p. 309) ; 
and at the caudal extremity of the males of Mermis 
albicans, mihi (Entom. Zeit. 1843, p. 79), there 
are, as in most Nematodes, two horny penises. 
But with Gordius, the structure of the genital 
organs is very different (see Siebold, and Dujar- 
din, loc. cit.)., In both sexes the cavity of the 
body is completely filled with a double genital 
tube, straight, and simple posteriorly, the sides 
of which aie formed of large cells. The genital 
* ($117, note 9.) For many details of the re 
productive organs of Ascaris infecta, with beauti- 
ful illustrative figures, see Leidy, A Flora and 
Fauna, &c., loc. cit. 4 B. Pl, VII. 14, 16, b. 19.— 
Ep. 
t1§ 118, note 2.] The view here suggested of 
opening is always at the posterior extremity of the 
body. The testicular tubes of Gordius aquaticus 
contain anteriorly, cell-like bodies ; but posteriorly 
there are others, staff-like, and which, being found 
among the eggs in the uterine tube, I have regarded 
as perfect spermatic particles. The genital open- 
ing of the male Gordius is between the two more 
or less prominent lobes of the caudal extremity, 
and is without copulatory organs. The simple, 
round, colorless eggs, are bound together at the 
posterior part of the uterus by an albuminous sub- 
stance, and are deposited in a very long row. It 
is this row of eggs which Léon: Dufour has 
described as Filaria filariae (Ann. d. Sc. Nat. 
XIV. 1828, p. 222, Pl. XII. fig. 4). 
1 See-Steenstrup, Ueber den Generationswech- 
sel, &c., 1842. 
2In various marine fish there is a trematode 
larva of a Tetrarhynchus (Miescher, Bericut 
ueber die Verhandl. d. Naturforsch. Gesellsch. in 
Basel. 1840, p. 29, and in Wiegmann’s Arch. 
1841, II. p. 3802), which would lead one to con- 
clude that alternate generation exists also with the 
Cestodes.t 
the alternating generation of the Cestodes, has. 
recently been confirmed most thoroughly’ by Sie- 
bold, who has treated the subject in a most come 
prehensive manner, in a Memoir in Siebold and 
Kailliker’s Zeitsch. II. 1850, p. 198.— Ep. 
