CLASSIFICATION. Xlil 



(Agassiz proposes the following classification, Contributions to Nat. 

 Hist., Vol. 1, page 185.) 



1st Class. Acephala, (orders as already given. ) 



2d do. Gasteropoda, with three orders, Pteropoda, Heteropoda, 



and Gasteropoda proper. 

 3d do. Cephalopoda, with two orders, Tetrabranchiata and 



Dibranchiata. 

 RADIATES. Four Classes. 



I. ECHINODERMS, (Gr. JEchinos, the Sea-urchin ; derma skin.) Four orders. 

 (1). HOLOTHURIDEA, (Gr. Holothourion,) Sea-slugs or Sea-cucumbers. 

 (2). ECHINIDEA, (Gr. echinos). Sea-urchins. 

 (3). ASTERIDEA, (Gr. aster, a Star.) Star-fish. 

 (4). CRINOIDEA. (Gr. krinon, a lily, lily-like). Encrmites. 



II. ACALEPHS., (Gr. akalephe, a nettle). Three orders. 



(1). PCLMONIGRADES, (pulmo, lungs ; gradior, to advance, t. e., con- 

 tracting or expanding their umbrella-shaped disk, thus showing 

 a resemblance to the motion of the lungs in breathing. 

 (2.) PHYSOGRADA, (Gr. phusao, to inflate ; gradior, i. e., supported and 

 moving in the water by means of one or more bladders, capable 

 of being filled with air at the will of the animal). Hydrostatic 

 Acalephs of Cuvier. 



(3). CILIOGRADA, (cilia, vibratile hairs ; gradior, i. e., moving by 



means of vibratile cilia disposed on the surface of the body.) 

 The orders are otherwise named thus : 



DISCOPHORA, (Disk-bearing) Medusae or Jelly-fish. 

 SIPHONOPHORA, (Siphon or Sucker-bearing, i. e., 



having aerial vesicles.) 



CTENOPHORA, (Comb-bearing, i. e., moving by vibrating 

 hairs resembling the teeth of a comb.) 



III. PHYTOZOA or ( (phut on, a plant ; zoon, animal, ^ Plant-like animals. 

 ZOOPHYTA, ( Two orders. 



Pol s \ ACTINOIDS, (aktin, a ray,) Ray-like animals. [animals. 



yp ' ( Hydroids, (hudra, a hydra or water-snake,) Hydra-like 



IV. PROTOZOA, (proton, first ; zoon, animal : i. e., the lowest form of or- 



ganized bodies.) 



[The last is a very numerous, but a very uncertain class. Linnaeus placed 

 them all at the end of Worms, and called them Chaos. So great is the 

 number of the INFUSORIES that they have sometimes been arranged into 

 Legions. Some have been transferred to the Articulates ; others have 

 been removed to the Vegetable Kingdom. Prof. Agassiz is of the opinion 

 that the entire class will soon be dispensed with. 



