BY GERARD KREFFT, ESQ., F.L.S. 209 



Order Til. Trematodbs. 



The body is parencliymatous and usually flafcteued. The 

 intestinal canal, which is often branching, has a mouth, but 

 nearly always is without an anus. The genital organs of both 

 sexes are combined in the same individual. Copulatory organs 

 are present. 



Genera : Gyrodactylus, Axine, Octobrothrium, Diplozoon, Polys- 

 tomum, Aspidocotijlus, Asjndogaster, Tristomum, Monostomum, 

 Holostomum, Gasterostomum. Peutastomum. 



Order IV. Acanthocephali. 



The sack-like body is flattened, transversely striated, and 

 swollen cylindrically by the absorption of water. Digestive 

 organs are wanting. The genital organs are situated in separate 

 individuals. Copulatory oi'gans are present. 



Genus : Eckinorlujnclms. 



Order V. Gordiacei. 

 The body is filiform and cylindrical. The digestive organs 



of these Proglottides takes place at the posterior end of the scolex by a 

 sexual reproduction, viz., by a simple process of growth and division. If we 

 compare this process with the phenomena of the alternation of generations, 

 we shall discover in it all the essential characters of the latter. The matured 

 joints or the sexual individuals of the Cestoidea in their proglottis form, pro- 

 duce a brood of embryos armed with six booklets (see plate III., figs. 22 and 

 23 of this paper — G.K.) which are quite dissimilar in shape from their 

 parents, the Proglottides, (see plate III., tig. 'lib of this paper — G.K.) and 

 remain so, since at a later period they assume the scolex form, and take on 

 the functions of an agamozooid. From the posterior end of the body of 

 such a scoliciform agamozooid a series of joints are developed, — that is to 

 say, a generation of sexual individuals which again present the original 

 proglottis form. In their organization the Proglottides, apart from their 

 sexual apparatus, so far resemble the scolices from which they have been 

 produced, that they possess no oral aperture, and moreover are subject to 

 a deposit under their integument of those glassy calcareous particles which 

 I have already mentioned. (A good idea of a young scolex will be obtained 

 by comparing the 2nd plate, figs. 25 and 2c, with the adult form figs. 2 and 

 2«— G.K.) It seems, at first, paradoxical to say that the joints of a tape- 

 worm which have hitherto been believed to be mere parts of one ani- 

 mal, should be considered as individuals ; but whoever will observe with 



