54 



THE TREMATODA 



embryo ; in this case the two are sisters, (c) The second embryo, or third 

 generation, is a " spore." 



FIG. III. Heterccotyleans. 



l.Microcotyle fusiformis, Goto, from the gill of Centronotus rululosiis (ventral view, after 

 Goto), a, buccal suckers opening into the oral cavity, behind which is the pharynx ; b, 

 common genital pore ; c, vaginal pore ; d, the lateral cotylophore with numerous small suckerlets, 

 each armed with chitinous skeleton. 



2.Monocotyle ijimae, Goto, from the oral cavity of Trygon postinaca (ventral view, after 

 Goto), a, mouth ; c, one of the eight compartments or loculi of the posterior sucker, which 

 is provided with a pair of small booklets Inserted in the hindmost pair of radii ; e, excretory 

 pore of the left side ; /, common genital pore ; g, vaginal pore, to the left of the middle line ; i, 

 intestine ; p, pharynx ; t, testis, here divided into three lobes ; y, the "sticky glands," which 

 functionally replace the anterior suckers. 



S.Diplectanum aequans, Dies, (side view after v. Beneden). a, the anterior end bilobed 

 and carrying a hook ; b, the left anterior, lateral sucker ; c, eye-spots ; d, great posterior sucker 

 armed with large hooks ; e, the rows of small spines in the wall of the sucker ; /, hooks. 



4. The same, anterior end, dorsal surface, c, eye-spot. 



5. The same, posterior end ; letters as before. 



6. Gyrodactylus elegans, v. Nordm., from gills of various fresh-water fish (after "Wagener) ; 

 ventral view, a, anterior lobe of the body which carries the pores of the " sticky glands " (b) ; 

 c, the mouth ; d, pharynx, lying in the pharyngeal sac ; the pharynx is eight-lobed, and each 

 lobe consists of an anterior clear portion and a posterior granular portion ; e, the intestine ; c', 

 mouth of first embryo ; d', the pharynx of first embryo ; /, uterus, with two embryos, one within 

 the other ; g 1 , the first embryo ; g", the second embryo within the first ; h, egg in oviduct ; 

 i, testis ; .;', ovary ; k, caudal disc, the margin of which is provided with a number of papillae, 

 each of which carries a booklet ; I, the great central hooks of the disc ; k', the caudal disc of 

 the first embryo ; k", the same of the second embryo. 



7. The same ; the everted pharynx seen from below, showing the eight tentacle-like 

 processes diverging through the oral aperture; the black centre is the entrance from the 

 pharynx to the cavity of the intestine ; the granular part of pharynx is not everted. 



8. The same ; one of the marginal hooks, a, the free end of the hook ; b, the plate to 

 which the handle e is inserted ; c, the hoop which serves for the attachment of muscles (d). 



Metschnikoff (34) has made an interesting comparison with the normal 

 development of Monostomum mutabile and other Trematodes. The result 



