THE CESTOIDEA 101 



amongst the Malacocotylea ; it is a new structure ; l whilst the 

 uterus functions in both orders as an egg-containing duct, to which 

 is added in the latter order the function of a copulatory duct. In 

 the whole of the Cestoidea, however, both these ducts can be 

 recognised ; but the original uterus is now employed exclusively as 

 a copulatory organ or vagina, whilst the original copulatory organ 

 has lost its function, arid, becoming greatly enlarged, serves as an 

 egg-containing duct, which, as we shall see amongst some of the 

 Merozoa, loses its external opening, and becomes a mere blind sac. 



If the identification of these parts is correct, and they have the 

 same relative position in the Ampliilina as they have in the Trema- 

 toda, this becomes still clearer on the reversal of the ordinarily 

 assumed position of the sucker, and we may therefore conclude that 

 the sucker of Ampliilina is homologous with the posterior sucker of 

 Heterocotyleans, and not with the anterior, as is generally assumed. 



G-yrocotyle also has a sucker at one end ; but in order to bring 

 the genital ducts and pores into agreement with those of AmpTiilina 

 and the Heterocotyleans, this sucker must be placed anteriorly when 

 that of Ampliilina is posterior. Hence, the suckers in the two 

 genera are not homologous, for that of Gyrocotyle corresponds with 

 the anterior sucker of the Trematodes, whilst the "rosette organ" and 

 its peculiar proboscis possibly represents the posterior caudal disc of 

 the latter class. In Gyrocotyle this position brings the paired excretory 

 pores anteriorly, as in the Heterocotyleans. We cannot at present 

 employ the nervous systems to aid us in comparison, for Spencer 

 and Wagener differ in their identifications of the " brain," which 

 leads to the difference in their mode of orientating the animal. It 

 is less easy to decide the point in Caryophyllaeus, for the male and 

 female ducts present quite peculiar relations (Fig. I. 1). The 

 male duct, instead of running alongside the vagina as in all 

 other | Cestoidea, runs towards it from the opposite end of the 

 body, and the three ducts open into a common atrium. If we 

 place the mobile organ posteriorly, and attempt to homologise it 

 with the rosette of Gyrocotyle, we shall have an anterior, median, 

 excretory pore, which position is unknown amongst the Trematodes, 

 though it exists in Eothrioplana. At the same time the relative posi- 

 tion of testis and germarium becomes that normal in the Trematoda. 



This rotation of the axis would lead to the assumptions (1) that 

 the " caudal vesicle " or tail with its six hooks in Caryopliyllaeus, and 

 therefore in the rest of the Cestoidea, is morphologically anterior, 

 a view already adopted by Grassi, and by Perrier, Blanchard, etc., 

 on quite other grounds ; and (2) that the suckers, etc., on the scolex 



1 Looss, however, while taking the above view with regard to the uterus of 

 Trematodes, holds (with Monticelli, Pintner) that the uterus of Cestodes is homo- 

 logous, not with the vagina, but with the genito-intestinal or Laurer's canal of the 

 Trematodes. While adopting Goto's views it has been deemed advisable in this 

 article to retain the usual names for these various ducts in the Cestodes. 



