APPENDIX. 



;23 



cavity containing both the viscera and the principal nervous cord, 

 the latter situated below the alimentary canal. The species 

 included arc Insects, Spiders, Centipedes, Crustaceans (or Crabs, 

 Lobsters, Shrimps and the like), and Worms. 



3. Sub-kingdom of IMOLLUSKS — or, as the name implies, species 

 having soft fleshy bodies, which are characterized also by a simple 

 bag-like structure, and by the absence of joints both from the body 

 and all appendages. As in Articulates, similar organs are repeated 

 on the right and left sides of a median plane, instead of around a 

 central axis ; but there is no succession of segments in the body, 

 or of corresponding ganglia (nervous masses) in the nervous 

 system ; and, consequently, Mollusks have not that composite 

 feature that characterizes and distinguishes Articulates. Examples 

 are the Oyster, Clam, Snail, Cuttle-fish, and Bryozoans (mentioned 

 on page 81). Many of the species have shells, as an external 

 covering ; but many also are without them. 



4. Sub-kingdom of RADIATES, the subject of this note. 



5. Sub-kingdom of Protozoans, briefly described on a following 

 page. 



The division of Radiates is thus the lowest but one in the system 

 of animal life, and its species are strikingly distinct from the 

 higher kinds in the radiate arrangement of the parts within and 

 without. 



Radiates are of three Classes. 



I St. Polyps., whose characters have already been stated (p. 3 and 

 beyond). 



2d. Acalephs, or Telly-fishes, or Medusae, as many of them are 

 called. Acalephs are often nearly transparent and jelly-like in 

 aspect, though not in consistence. They have sometimes the shape 

 of a disk, convex above, or a hemisphere, or a bell-shaped 

 spheroid, and vary in diameter from a fraction of an inch to three 

 yards or more. Attached either to the margin, or to the under 

 concave surface about the mouth, there are usually four tentacles 

 or groups of tentacular appendages, or a continuous fringe of 

 tentacles ; or there are other tasselings beneath the pellucid body ; 

 and these organs, like the tentacles and some other parts of an 

 Actinia, are furnished with myriads of lasso-cells. The whole 

 structure is as completely radiate within and without as that of a 

 Polyp ; but there are radiating, and radiately branching, vessels 

 passing outward from the stomach cavity instead of radiating 

 compartments. Acalephs, or jelly-fishes, float in the ocean, usually 

 with the mouth downward, moving ordinarily by the contraction 

 and expansion of the sides of the body. Hydroids (p. 76) are 

 sexless forms under one division of Acalephs ; they are usually 

 attached, and look like polyps. 



3d. Echinodervis. Examples of this class 2Lre,Jirsf, the star-fishes., 

 oxjivc-fingcrs, whose bodies, although containing calcareous plates, 

 are somewhat flexible, and ordinarily either five-rayed (fingered) or 

 five-angled (but sometimes more than five) : — seco)id\}[^Q Echinus or 



Y 2 



