492 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



Holothurians reduction is carried still farther, the 

 genital tubes finally uniting into a single tube which 

 opens near the anterior end of the body. 



In keeping with their 

 other primitive characters, 

 the Crinoidea have a more 

 diffused arrangement of 

 the genital glands ; these 

 are situated in the axis of 

 each arm, and make their 

 way into the pinnulse that 

 are attached to it (Fig. 

 205). 



It is ordinarily sup- 

 posed that the generative 

 products of all Echino- 

 derms make their way in to 

 the water in a more or less 

 casual manner ; in Aste- 

 rina, however, Ludwig has 

 observed that the males 

 twist their arms around 

 those of the female, and so 

 dispose themselves as to 

 ensure the escaping sper- 

 matozoa meeting with the 

 ejected ova. A somewhat 

 similar mode of copulation 



Fig. 205. Cross Section of a Pinnule 

 of the Arctic Feather-star (An- 

 tedon eschrichti] ; x 75. 



has been observed by Jic- 

 keli in Antedon rosacea. 

 In addition to their 



a, Axial cord; a', its branches ; ag, ara- 

 bulacral or food groove ; b, radial 

 blood-vessel; w, radial nerve; ov, 

 ovary ; pj, joint of pinnule ; w, water- 

 vessel ; T, tentacles. (From P. H. Car- ., .. . 

 penter.slightly altered from Ludwig.) power Ol SCXUal multi- 

 plication, the Echinoder- 



mata are distinguished by their remarkable capacity 

 for repairing injuries, and of giving rise to new indi- 

 viduals from separated arms ; in those cases in which 

 the rays are very numerous (Brisinga, Labidiaster), 



