SECT. VI. 



ECHINODERMA TA. 



181 



Pig. 141. Spine of Echinus 

 miliaris. 



spine perpendicular to its axis exhibits a succession of 



concentric rings like those of an exogenous tree. The 



cup at the bottom of the spine is 



very dense network, and the last 



of a sheath of encircling pillars 



form the ribs, sometimes seen on 



the exterior of the spines. 



The spines of the Echinus 

 miliaris, of which fig. 141 repre- 

 sents the segment of a section 

 highly magnified, are fluted co- 

 lumns of calcareous glass, the 

 grooves of which are filled with 

 solid glassy matter curved on the 

 exterior. The innumerable hair- 

 like objects attached to the shells 

 of some of the Echinidse, the 

 almost filamental spines of others, and the pedicellarise 

 themselves, are formed of a regularly reticulated sub- 

 stance. When the Echinidse are stripped of their spines 

 and all their appendages, 

 their shells show 2,400 

 plates united with the 

 symmetry of a tesselated 

 pavement. 



The Echinidse are male 

 and female, and the eggs 

 are excluded through the 

 five perforated productive 

 plates at the posterior end 

 of the shell. According to 

 the observations of Prof. 

 Fritz Muller the embryo, 

 soon after issuing from the 

 egg, takes a form repre- 



1 4 . 



n 



fonr arms of the Platens-body; e, cal- 

 careous framework; /, ciliated lobes; 

 ffffffff, ciliated processes of the proboscis. 



