168 ‘CLASS Y. 
The testes have mostly a rounded form; in Amphistoma subtrique- 
trum and giganteum, they are finger-shaped and branched!. From 
these testes, usually two in number, efferent vessels proceed to a 
seminal vesicle lying at the base of the penis in the Cirrus-sac 
(receptaculum Penis); from which a canal arises that runs to the penis. 
But besides this, one of the testes gives still a third vas deferens to 
a seminal vesicle lying further behind (vestcula seminalis interior), 
and from which arises a short tube connected with the oviduct?. 
Here self-impregnation may be effected: in which case the second 
vesicula seminalis and the external genital organs are difficult of 
explanation: unless we suppose that both self-impregnation and 
copulation are possible. In the female organs of the suctorial worms 
we would direct particular attention to that remarkable arrangement 
by which, according to V. SreBoLD, the yolk and the germ (vesicula 
germinativa) are not produced in the same organ:—that here we 
must consequently, instead of ovary, distinguish a germ-stock and a 
yolk-stock. The lateral parts, usually dendritic or botruoidal, which 
were formerly believed to be ovaries, are the yolk-stocks: the germ- 
stock is placed in the middle of the body, and has a roundish form. 
In the Tape-worms the two sexes are also united: and V. SreBoLD 
suspects that in this case, also, the germ and yolk-stocks are dis- 
tinct organs. In the jointed T'ape-worms (Tenia, Bothriocephalus) 
the sexual organs are situated in every joint, only the anterior more 
recent joints do not yet indicate them, because they become more 
perfectly developed in proportion as the joints are more posterior. 
These animals, therefore, during their growth present us with a 
successive repetition of the same organisation. Some authors think 
that every individual joint is to be considered as a suctorial worm, 
and the T'ape-worm as a compound suctorial worm. The sexual 
openings are situated in every joint, either on the edge or in the 
middle. In Bothriocephalus latus, for instance, on the abdominal 
surface of the body there is a fold of skin in the middle of each 
1 Amphistoma triquetrum, Bosanvs Isis, 1821, transferred to Scumauz Tabul. 
Anatomiam Entozoor. illustr. Dresde, 1831, Tab. vil. figs. 7—9; Amphistoma gigan- 
teum, DiEstne in Wiener Annalen 1. Tab. Xxtt. figs. 9, 14, 15. 
2 V. Srmpoxp found this arrangement in many species of Distoma, and suspects that 
it occurs in all. See BuRMEISTER on Distoma globiporum in WincM. Archiv. 1. 1835, 
s. 187; V. Sresoxp, ibid. 11. 1836, s. 217, Tab. vi., and in MuELLER’s Archiv. 1836, 
§. 235—237, Distoma nodulosum, Tab. X. fig. 1. 
