JTION V 

 PHYLr.M PLATYHELMINTHES 



A NVMBER of c! ''.etazoa, some a little, others very de- 



cidedly, higher is nation than the Coelenterata, are commonly 



regarded as coi> one great sub-kingdom or phylum the 



Vermcs or Worn.- oroups ordinarily referred to the Vermes. 



differ, however, very widely from one another: points of agree- 

 ment, except sucl merely negative, are, in fact, frequently 

 hardly recoe , rather than group together under one 

 common de- i such a heterogeneous assemblage of forms, it 

 si 'cms be1 d the term Vermcs altogether and to endeavour 

 to divide th as 1 ' into phyla the members of which shall 

 have points of p, itive resemblance to one another. The four 

 phyla Pint [i "'.<?, Nematkelminthcs, Trochelminthes, Mollus- 

 coida, and A . with their appendices, all consist of forms 

 which are or hav been comprised in the Vermes. They differ 

 from tb ita in the presence of three well-developed 

 body-layers - () f \\Jiich the middle one, or mesoderm, is of relatively 

 predoiu: , portance: and, for the most part, in the much, 

 higher si complexity attained by the various systems of 

 organs. -ur phyla present no metameric segmentation: 

 in th A . metamerism is more r less strongly pronounced. 



. T / intltes or Flat-Worms are a group of soft-bodied, 



bilr i\* flattened animals, which are devoid of true 



metal ^.aentatioii (p. 41). With a sufficient degree of uni- 



formi Tucture to render the phylum a fairly compact and 



well one, there is yet a considerable range in complexity, 



fron ; -st forms, certain of which have been supposed to be 



nea i-red with the Ctenophora among the Coelenterata, to 



vhich have all the various systems of organs very 



highly developed. The body is built up from 



-. v-nic layers sctoihr'in, mesoderm, and civlodcrm as in 



