APPENDIX 



CLASSIFICATION OF TYPES. 



THE broadest division of the typical organisms considered in 

 this volume is into Protozoa, or organisms which are unicellular, 

 and Metazoa, or organisms which are multicellular, and in which 

 there is physiological division of labour and morphological differ- 

 entiation of structure among the cells. To the protozoa belong 

 the amoeba, destitute of a mouth, and possessed of the power of 

 emitting pseudopodia (Rhizopoda\ the vorticella and paramce- 

 cium (Infusoria ciliata), with ciliated bodies, and provided with 

 a vestibule or oral fossa, and the monads (Infusoria flagellata), 

 with one or more whip-like processes or flagella. The other 

 organisms here considered belong to the metazoa. 



The metazoa again are divided into Codenterata, to which 

 the hydra belongs, in which there is no true body cavity and 

 in which the symmetry is radial, and Coslomata, in which a body 

 cavity or coelom is present. 



The ccelomatous forms are roughly divided into the Vertebrata, 

 in which an endoskeleton is developed, the axial portion of 

 which consists of the skull and vertebral column, and the In- 

 vertebrata, in which an endoskeleton so constituted is absent. 

 The Invertebrata form a very heterogeneous group, distinguished 

 merely by negative characters. Those which we have considered 

 fall into three divisions. 



(1) The Arthropods, with bilateral symmetry, segmented 

 bodies, jointed lateral appendages, and a ventral nerve-chain. 

 To this group belong the crayfish, a decapod crustacean, breath- 

 ing by means of branchiae, in which the body is divided into 

 cephalo thorax and abdomen ; and the cockroach, an orihopter- 

 ous insect, in which respiration is by tracheae, and the body 

 is divided into head, thorax, and abdomen. 



(2) The Termes, with bilateral symmetry, unsegmented (liver- 

 fluke) or uniformly segmented (earthworm) body, with lateral 

 appendages which (when present) are not jointed, and with 



