88 



THE SCIENCE OF LIFE. 



jointed spines, scattered all over the shell of the Echinus, 

 and terminated by a three- fold claw, capable of being 



FIG. 89. Morphology of Echinoidea. i. Portion of the test of Galerites hemisphericus 

 enlarged, showing the inter-ambulacral area (a) and the ambulacral areas, (.) 2. Galer- 

 ites hemisphericus viewed from above, a. Inter-ambulacra, b. Ambulacra. 3. Genital 

 and ocular disk of Hemicidaris intermedia, enlarged, c. Ocular plate, d. Genital plate. 

 e. Anal aperture, f. Madreporiform tubercle. 4. Spine of the same. (After Forbes.) 

 The tubercles are mostly omitted on figs. 2 and 3 for the sake of clearness. 



closed like a pair of forceps upon animalculae or other 

 offensive matter that may tend to obstruct its shell. One 

 carries the rejected matter to another till the surface is 

 completely free. 



The mouth of an Echinus contains the most complex 

 and perfect dental apparatus in all the Animal Kingdom, 

 although occurring in a type generally considered of a 

 low grade of structure. It sets at naught all theories of 

 Evolution, since in our progress from the simplest forms 

 of life it is the first instance of a dental apparatus, and 

 the most perfect of all. It is composed of five accurately- 

 htting vertical pyramids, each provided with a rod-like 

 tooth, worked by a couple of beautifully arranged mus- 

 cles. (Fig. 90.) The intestine is tortuous and connected 



