Lesson XIII.] 



NATURAL HISTORY. 





therefore they have been divkled into three 

 f.nnilies. 1. The Attervu, or star-tish. 

 2. The Erhinida, or sea-eggs. 3. The 

 IIu!o!tiuri<r, or sea- slugs. 



/'.Describe the star-fishes. 

 P. The mouth is on the underside, and 

 licijiit! lu-rve surrounds it, and sends 

 ot!' iilainenis to eacli arm or ray [see Fig. 

 21] ; the anus or rays are five in number, 

 :ieciesare covered with osseous 

 c Miles furnished with strong 

 moveable spines. 



17'.. T. What is there peculiar about 

 the sea-eggs ? 



P. The body is enclosed in a calca- 

 reous shell, composed of various segments, 



fig. *>. 



which fit closely together, and are arranged 

 in alternate rows of plates, with tubercles to 

 which the spines are at- 

 tached, and perforate i 

 plates for the mem- 

 braneous feet to pass 

 mouth 

 -'i.d with live 

 flat, calcareous terih, 

 winch are pointed 

 with hard enamel. 

 The whole dental ap- 

 paratus consists of 

 twenty - five 

 J*f . i. t 

 -, which < animal to 



H. Kckinut, or tea-urchin; the right 

 tide covered wilh tpmea ; (he left hat them re- 

 moved to how the pUte* of the hell. 



t Fig. 24. The Uttfa of Ma-urchin, showing 

 their arrangemrut. 



crush the shells of the fish on which it 

 feeds. 



176. T. Can you tell me anything about 

 that curious animal, the Sea-slug .' 



P. The flololhurue are sometimes called 

 " sea-cucumbers," and have a number of 



Fig. 15. 



curious looking tentacula distributed over 

 their bodies, which they can retract at 

 pleasure. They have a leather-like skin, 

 with an aperture at each end, and a most 

 complex structure. 



177. 7". NVh.it is the second order 

 called? 



P. APODA, or animals witho; 

 which are chiefly found in th 



nd resunhle the II iol/iurt.r, 

 with the exception of their skin, which 

 is devoid of tentacula, and the \\.iui 



GENERAL QUESTIONS ON LESSON 



1. NV-i.it is t'.ir :.e last great 



ii of anima; 



i.ils arranged 

 last? 



>w are the Iladiata divi 



1. N\ 



DERMATA ? 



5. Is there anything peculiar in the 

 nervous syti : lass? 



the first 

 >f bristly-sk dsf 



lie reason the animals in (his 

 ive been eparat< others. 



Fig. K.-Hololk*ria. howin< the t. 

 amond In rows on the surface of the UUj, 

 nd ihe irce-hke mpiralury vr*m 



