450 THE CAT. [chap. xiii. 



families and genera. Eacli of tliesG groups is in all cases defined (as 

 before said) by the common structural characters which the creatures 

 included within it possess. Tlie groups become successively smaller 

 and smaller (in the number of species they contain) as we descend 

 from any sub-kingdom through its classes and orders to its families 

 and genera. In other words the groups become successively smaller 

 in their extent. In each case the technical name given to a group 

 denotes the animals contained within it, and connotes the common 

 characters which pertain to the group. Obviously then, the larger 

 and more primary the group, the greater the number of kinds 

 denoted by it [i.e. the greater its extension), and the less the number 

 of common characters connoted by it {i.e. the less its intension). 

 Obviously also, the ultimate groups, e.g. " species," have the least 

 extension, but imply, or connote, the greatest number of common 

 characters, i.e. they have the maximum of intension. 



§ 8. Now the animal kingdom (as generally understood) is 

 divisible into eight sub-kingdoms, apart from that to which the 

 cat belongs. Thus there is the sub-kingdom (I.) Hypozoa, which 

 includes all the lowest, so called, animals, such as Aniocba3, Fora- 

 minifera, Radiolaria and Flagellate animalcules — together forming 

 the Rhizopoda — with the lowly parasites called Gregorinida, and 

 all Infusoria. (11.) Secondly, there is the sub-kingdom of 

 Sponges, SroNGiDA. Next comes (III.) the sub-kingdom which 

 includes the Hydra and Sea-anemone, together with all Jelly-fishes, 

 Sertularians, coral-animals and such creatures as Beroe and the 

 Cestum Veneris. This great sub-kingdom is that of the Ccelentera. 

 Then there is (IV.) tlic sub-kingdom Echinoderma, which includes 

 the star-fishes, sea-urchins (or sea-eggs), brittle-stars and the sea- 

 cucumbers, some of which are known as the Japanese edible, 

 " Trepang." Next (Y.) comes the very numerous sub-kingdom of 

 Worms, Vermes, amongst which are to be reckoned not only earth- 

 worms, leeches, sea-mice and tube-worms — these four forming the 

 Annelids — together with tape- worms and thread- worms ; but also 

 the flukes (or Trematoda), the TurhclJaria, the Bryozoa (or Po/i/zoa), 

 the wheel-animalcules (or lioti/era), the singularly primitive worm 

 Dicyema* together with Balanoglossus (type of the Enteropnemata) 

 and the active marine Sagittd, with worms allied to the Echino- 

 derma and called Gepliyrca. Then we have (VI.) the sub-kingdom 

 Arthropoda, largely exceeding, in the number of its species, all 

 other sub- kingdoms put together. It includes the crabs, lobsters 

 and shrimps, the centipedes and millipedes, the spiders, scorpions, 

 tics and mites, and all the vast multitude of Insects. We have also 

 (VII.) the sub-kingdom Mollusca, containing all the cuttle-fishes, 

 pteropods, snails and whelks, oysters, scallops, &c., with the curious 

 lamp-shells. Lastly Ave have (VIII.) the sub-kingdom Tunicata, 

 containing the seemingly senseless forms already noticed as Tunicates, 

 with a number of other species ; all of which are often called Ascidians. 



* Described by Prof. E. Van Bcneileii, i "Eechcrclicssm-lesDicyemicl.T. " It may 

 Bull. Acad, lielg. xli., xlii., 1876, | be the typo of a distinct sub-kingdom. 



