CHAPTERS ON EVOLUTION. 



nervous system in three great masses (Fig. 6, h, i, ), as well as 

 by other definite characters writ large enough in the textbooks of 

 zoology. These animals form the type of the Mollusca a group 

 from which many animals therein included by Cuvier have been 

 weeded out to form other divisions, or to find a place in other 

 types. Similarly, the fact that the star-fishes, sea-urchins, sea-lilies, 



sea-cucumbers, and 

 the like, form another 

 and distinct type 

 (Echinodermata), dis- 

 tinguished by the 

 "radiate" shape of 

 the body, and by 

 other characters, 

 might be dwelt upon. 

 A diagram of the 

 FIG. IT. AMCEB^. star-fish type is shown 



a, Amoeba radiosa; b. Amoeba diffluens, in various stages of -r- i j 



contraction. in Pig. 7, C. It WOUld 



merely extend our 



illustrations to show how the hydras (Fig. 8), zoophytes (Fig. 9), 

 jelly-fishes (Fig. 10), corals, and sea-anemones form another " type " 

 ( Calenterata), noted for its curious digestive system (Fig. 7, B e), 

 which communicates freely with the internal cavity of the body 

 (B/). Whilst, last and lowest of all, the Protozoa, represented by 

 the sponges, Amoeba (Fig. n), the Foraminifera or chalk-animal- 

 cules (Fig. 12), and many other and equally simple forms of animal 

 life, constitute the lowest type. These animals are distinguished 



rather by their want of organs 

 and tissues than by the posses- 

 sion of the belongings of higher 

 animals, and exhibit bodies which 

 consist, for the most part, of 

 simple masses of protoplasm, but 

 which, nevertheless, exhibit all 

 the fundamental characteristics 

 of living organisms. The diagram of a Protozoon might thus be 

 adequately enough rendered by a simple figure representing an in- 

 definite mass of protoplasm, such as is represented in Fig. 7, A. 

 It will thus be seen that the four Cuvierian " types " have become 

 largely extended and modified by modern research. But, notwith- 

 standing these modifications, the principles whereon that great 

 anatomist laid the foundations of the constitution of the animal 

 world, remain solid and enduring as of old. If to-day our list of 

 types is of a more extensive character than was the Cuvierian 

 repertoire, it must be borne in mind that such a result was in- 



Fic. 12. FORAMINIFERA. 



