120 THE HELMINTHES. $ 115. 
the genital organs of the first is yet imperfectly known; while that of those 
of the second is well understood. The female apparatus of the Tremato- 
des consists of a germ-forming organ (ovary), with its excretory duct; 
then, two others for forming the vitellus, which have also excretory 
ducts; and then a simple uterus with its vagina. The male apparatus con- 
sists of testicles with their excretory canals, an internal seminal vesicle, a 
cirrhus-sac, an external seminal vesicle, and a penis. 
The ovary consists of a round or pyriform ® yeservoir, situated, usually, 
upon the median line of the body, from which it is distinguished by its 
pale color and transparency. It is filled with simple round cells— the 
egg-germs, The nucleus of these cells is the germinative vesicle, and the 
nucleolus, the germinative dot. 
The short and small excretory duct of the ovary opens at the commence- 
ment of the uterus. The organs which secrete the vitellus are two in num- 
ber, of variable length, and situated upon each side of the body near the 
dorsal surface; they occupy either the cervical, the central, or the posterior 
portion of the animal, and sometimes extend over them all. They are 
nearly always composed of ramified caeca filled with white, granular. 
vitelline corpuscles. By reflected light these caeca appear through the 
‘skin as a white, ramified, botryoidal mass, and from each of them, pass 
off inwardly, numerous excretory ducts, which retinite opposite the ovary 
into two common canals, These last approach each other transversely, 
and form a single canal upon the median line, which, after a short course, 
opens at the bottom of the uterus by an orifice which is common to it and 
the ovary.” 
Pentastomum taenioides, organs which are re- 
garded by Diesing as caeca for secreting the en- 
-velope of the eggs. 
Since all the parts of the genital organs of Pen- 
tastomum have not been examined with this same 
precision, I can give no opinion as to their use.* 
2 See Siebold, in Wiegmann’s Arch. 1826, I. p. 
217, Taf. VI., and in Miller’s Arch. 1836, p. 232, 
Taf. X. fig. 1. 
3 The ovary here is always smaller than the 
testicle, and sometimes as to form very closely 
resembles it, as in Distomum globiporum, and 
dongicolle, mihi (from the urinary bladder of 
Cottus gobio); consequently it may easily be 
‘taken for a third testicle. 
4 With Monoastomum, it lies wholly at the pos- 
terior extremity. 
5 In Polystomum, Octobothrium and Diplo- 
oon, the germs are so large that they may easily 
de taken for perfect eggs. 
There is here, moreover, between the cell-wall 
zand the nucleus (the germinative vesicle), quite a 
thick layer of albuminous substance, somewhat 
* (§ 115, note 1.] See upon this subject Van 
Beneden (Ann. d. Sc. Nat. XI. 1849, p. 326), who 
thas described in detail the sexual organs of Lin- 
guatula Diesingii, and has shown the sexes to be 
separate. See also my note under § 99.— Ep. 
+[§ 115, note 7.] To say that certain organs 
secrete vitelline cells, is a little obscure, and no 
doubt Siebold intended to convey the meaning 
that they secreted the plastic material out of which 
these cells are formed. I make this perhaps 
seemingly unnecessary reference to the matter, 
since it concerns the subject of the development of 
the ovum. In the Ascaris, where the origin and 
development of the ovum can be satisfactorily 
representing a vitellus. But in the other Trema- 
todes it is so thin as scarcely to be perceived. 
6 With the following Trematodes there is a wide 
deviation from this usual arrangement. In Dis- 
tomum longicolle the organs producing the 
vitellus are two simple round caeca located behind 
the ventral sucker; in Distomum cygnoides, 
they are two very small deeply-fissured bodies ; 
and in Distomum gibbosum, there is one only, 
which is star-shaped and located at the middle of 
the body. 
7 These organs, until now regarded as ovaries, 
secrete only vitelline cells. With most Trematodes 
their nuclei are clear, and have been taken for 
eggs. In eggs recently formed, one can always 
distinguish these cells from the germs. In passing 
the excretory canals they are compressed and 
elongated, but never run into each other. When 
these canals are crowded, they have the aspect of 
white cords, which have often been taken for 
nerves. But when they are empty, they, as well 
as ag vitellus-secreting organs, are almost invis- 
ible. 
studied, you first notice the germs as nucleolated 
cells, of which the nucleus is the future germina- 
tive vesicle and the nucleolus the germinative dot. 
These cells increase in size, and as they move 
along there appear in the liquid which lies between 
the nucleus and the cell-wall minute granules 
which ultimately become cells; in this way the 
Vitellus is formed, the formation being enCogenous 
and not exogenous. These special organs or 
tubes therefore are vitellus-forming organs, in vir- 
tue of their secreting the formative material out 
of which the vitellus is formed within the original, 
nucleolated germ-cell. — Ep. 
