THE CESTOIDEA 99 



included will be found in (30). Of the various genera included in 

 the grade, it is Amphilina that appears to be the most primitive in 

 its anatomy, though Leuckart sees in " Archigetes " an archaic form ; 

 but in its general anatomy there is here a greater divergence from 

 the Trematodes than is seen in Amphilina. 



It is usual to regard the single sucker of all these genera as 

 homologous throughout, and to place it anteriorly ; but if we have 

 regard to its position in relation to the genital pores, it is possible 

 to deny this homology. Spencer (46) and Lonnberg, though with- 

 out definitely expressing any general dissent from the usual view, 

 place the sucker of Gyrocotyle at the posterior end, whereas Wagener 

 and others place it anteriorly. 



If we examine the genital organs and ducts in Amphilina, on 

 the one hand, and any Heterocotylean Trematode on the other, 

 we shall see that the comparison is very much more easily appreci- 

 ated if the sucker of the former be placed posteriorly instead of 

 anteriorly as is customary. 



In Amph. foliacea the sucker is at the pointed end (Fig. II. 1) ; 

 the male pore is at the opposite extremity; the penis is armed 

 with ten booklets ; the vas deferens soon bifurcates, and its branches 

 are distributed to the marginal, follicular testes. The germarium 

 is single ; the short germ-duct opens into the ootype, which com- 

 municates with three canals : (a) the short, common vitello-duct ; 

 (/?) the egg-containing duct or " uterus," which is a long undulating 

 canal opening externally close to the sucker ; and (y) a short 

 " vagina " or copulatory canal, which opens near the male pore. In 

 A. liguloidea there is a fourth canal (8), which runs in the opposite 

 direction and ends blindly ; it is known usually as the " anterior 

 vagina." 



Now in the Heterocotylean (see Fig. I. p. 51) the germ- 

 arium lies anteriorly to the testes ; the sperm -duct and the 

 uterus (or egg -containing duct) run forwards side by side to 

 open near the anterior end of the body, either close together 

 or into a common atrium. The vitellarium is identical in 

 Cestodes and Trematodes, the vitelline duct opening into the 

 oviduct opposite to the junction of the latter with the uterus. 

 Arising close to this point there is in the Heterocotylea the 

 vagina or copulatory duct, whose external pore is independent 

 of the uterine or birth-pore, and generally posterior to it. More- 

 over, the genito- intestinal canal (Laurer's canal) communicates 

 with the oviduct in the same region. Now, turning again to 

 Amphilina, the female copulatory duct or " vagina " has the same 

 topographical relation to the other parts of the apparatus as the 

 " uterus " or egg-containing duct of Trematodes ; and the " uterus " 

 of the Cestode corresponds with the " vagina " (when present) of 

 the Trematode. Further, the " anterior vagina " of A. liguloidea is 



