OPHIOPHOLIS ACULEATA 187 



the oral surface of the central disc in the madreporic plate already 

 mentioned. There are four Polian vesicles attached to the ring 

 canal. Tiedemann's bodies are absent. In each arm are only 

 two rows of ambulacral tubes and they are developed as ten- 

 tacles, devoid of a sucker and useless in locomotion. The dif- 

 ference in the number of rows is, however, not of great impor- 

 tance, since we must remember that in the starfish there are al- 

 ternating longer and shorter transverse canals, while in the brit- 

 tle star all transverse canals are of the same length. The ner- 

 vous system is more differentiated than in the starfish. The 

 radial nerves have regular ganglionic enlargements in each seg- 

 ment of the arm; the dermal network of the ectoneural system 

 has disappeared. Eyes are absent, but the terminal tentacle is 

 present in each arm. 



Ophiopholis aculeata reproduces with a metamorphosis, in 

 many respects similar to that of the starfish. The sexes are sep- 

 arate and the reproductive cells are discharged into the water. 

 The larva which develops from the fertilized egg is provided with 

 two long and four short arms and is known under the name of 

 Pluteus. 



Instructions 



1. Make a half page drawing of the aboral surface showing 

 central disc and arms. Label all plates on the central disc. 



2. Make a drawing, on the scale of 5:1, under dissecting 

 microscope, of a few segments of an arm, showing dorsal plates, 

 row of scales separating them, lateral scales and the spines on 

 the lateral plates. 



3. Make a half page drawing of the oral surface showing oral 

 pentagon with teeth, five arms, genital slits. 



4. Make a large drawing of the ventral surface of the disc, 

 examining it under dissecting microscope. Label oral pentagon, 

 fringe of oral papillae or scales, jaws with teeth, oral tentacles, 

 adoral and oral plates, madreporic plate, genital slits, ventral 

 plates of the arm, ambulacral pores, tentacle scales and tentacles. 



