THE CESTOIDEA 97 



but there are certain genera which consist of a single segment and 

 have only one set of genital organs. This group of forms only 

 differs materially from certain Trematodes in the absence of the 

 enteric cavity, and constitutes a lower grade, from which the 

 segmented Cestodes are derived. 



This grade is the Monozoa, and the second grade may be termed 

 the Merowa. 



GRADE A. CESTOIDEA MONOZOA, Lang ( = Cestodaria, Montic. ; 



= Cestodes monogeneses, v. Ben.; = Atomiosoma, Montic.). 



Cestoidea, in which the animal consists of a single segment, con- 

 taining a single set of reproductive organs. In addition to the 

 male pore and female (vaginal) pore, there is a third aperture, 

 that of the uterus (birth-pore). The apparatus by which fixation is 

 effected consists, usually, of a single sucker, but presents considerable 

 variation in form, as well as in disposition, with regard to the genital 

 pores. 



ORDER 1. Amphilinacea. 



FAMILY 1. AMPHILINIDAE. Oval or leaf-shaped, without a distinct 

 " head " ; with a single small acetabulate sucker at one end. Amphilina, 

 "Wagener ; A. foliacea, Rucl., in the sturgeon (see 39), (Fig. II. 1) ; A. 

 liguloidea, Dies., in fresh-water fish, Brazil ; Wagneria, Montic. ; W. pro- 

 glottis, Wagn., in the intestine of Scijmnus nicceensis. 



ORDER 2. Gyrocotylacea. ! 



FAMILY 2. GYROCOTYLIDAE. Leaf-shaped, with crenate margins. At 

 the pointed extremity is a small but deep sucker ; at the opposite end is 

 a " rosette organ " carried by a cylindrical peduncle, traversed by a canal 

 opening at each end, from which a peculiar proboscis-like organ can be 

 everted. Gyrocotyle, Dies. ( = Amphiptyches, Wagn.), (see 46); in the 

 intestine of Chimaera and Callorhynchus (Fig. II. 4). 



ORDER 3. Caryophyllacea. 



FAMILY 3. CARYOPHYLLAEIDAE. Elongated, cylindrical worms, either 

 with a single sucker or without one, and then with one end capable of 

 considerable mobility. Monobothrium, Dies., with a single terminal sucker ; 

 M. tuba, Wagn., in the intestine of Tinea chrysitis ; Caryophyllaeus, Mull., 

 without a sucker, but with a characteristic mobile organ, capable of being 

 thrown into undulatory folds, giving the appearance of a " clove-pink " ; 

 G. mutabilis, End. (Fig. I.), in the intestine of Cyprinoid fishes, and 

 (young) in the coelom of Tubifex, in segments 8 to 20 (see 50). The 

 worm described by Leuckart as Archigetes sieboldii, from the genital seg- 

 ments of Tubifex rivulorum (see 23), is in all probability only the 

 immature phase of Caryophyllaeus. The cylindrical body carries a tail 

 provided with three pairs of booklets, thus resembling the " caudal 

 vesicle " of such a Cestode as Taenia solium ; it has been suggested that 

 it is a permanent " cysticercus form " with the head everted. The head 



