168 CLASS V. 



The testes have mostly a rounded form ; in Amphistoma subtrique- 

 trum and giganteum, they are finger-shaped and branched 1 . 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 (vesicula seminalis interior), 

 and from which arises a short tube connected with the oviduct 2 . 

 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. SIEBOLD, 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 Y. SIEBOLD 

 suspects that in this case, also, the germ and yolk-stocks are dis- 

 tinct organs. In the jointed Tape- worms (Tcenia, 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 Tape-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, BOJANUS Isis, 1821, transferred to SCHMALZ Talul. 

 Anatomiam Entozoor. illustr. Dresdae, 1831, Tab. vm. figs. 7 9; Amphistoma gigan- 

 teum, DIESING in Wiener Annalen I. Tab. xxn. figs. 9, 14, 15. 



2 V. SIEBOLD found this arrangement in many species of Distoma, and suspects that 

 it occurs in all. See BURMEISTER on Disloma gloliporum in WIEGM. Archiv. i. 1835, 

 a. 187 ; V. SIEBOLD, ibid. n. 1836, s. 217, Tab. vi., and in MUELLER'S Archiv. 1836, 

 g. ^35 737, Distoma nodulosum, Tab. x. fig. i. 



