IOO 



GENERAL PRINCIPLES OF ZOOLOGY 



FIG. %2. Haliottiniu erinaceus. it, external. /, internal, latticed spherical skeleton; cA, cen- 

 tral capsule; -wk, extra capsular soft parts; , nucleus. 





FIG. 83. Nausithoe, an acrasped medusa (after Lang), seen from the end of the greatly- 

 shortened main axis, pr, perradii ; jV, interradii ; ar, adradii (perradii and interradii 

 mark the four planes of symmetry of the animal); sr, subradii ; rj, mantle-lobes : /, ten- 

 tacles ; s, sensory organs : g, sexual organs ; gf, gastric filaments ; m, subumbrellar cir- 

 cular muscle ; m the centre the cross-shaped mouth-opening. 



