THE DEVELOPMENT OF ASTBRINA GIBBOSA. 261 



have greatly developed, and have grown in between the radii on 

 to the oral surface^ forcing the original oral plates to the extreme 

 centre of the disc ; and so the stone-canal has been swung round 

 and the genital rachis pulled out of shape. Now in Asterina 

 gibbosa there is a trace of this process; the rachis does 

 not, as Hamann (7) has described in Asterias, lie in one plane, 

 but pursues an undulating course, being much more aboral in 

 the radii than the interradii. I am inclined to look upon this 

 as the primitive condition from which the Asterid and Ophiurid 

 arrangements have been derived. I may as well mention here 

 some other facts which indicate the primitive nature of Asterina. 

 Chief among them is, that in the family of which it is a member 

 we meet with the most rudimentary form of those characteristic 

 Asterid organs the pedicellarise. We have in Asterina the 

 aboral surface covered with small spines, arranged in twos and 

 threes, and acting on irritation like pedicellariae. It is true 

 that some Asterids have no pedicellariae, but here the evidence 

 from allied genera (cf. Luidia and Astropecten) suggests that 

 they have been lost; Asterina, however, shows us pedicellariae 

 in statu nascendi. The simple biserial tube-feet also con- 

 stitute a primitive character. 



Fig. 118 represents ovoid gland and stone-canal in the 

 latest stage examined by me. The gland is attached by an 

 exceedingly narrow pedicle to the wall of the axial sinus. 

 Its surface is thrown into deep folds, and the peritoneal 

 lining of the axial siuus, which forms its outer covering, is 

 modified, consisting of cylindrical cells with projecting rounded 

 ends. The interior of the gland is filled with a mass of primitive 

 germ cells supported by fibres, doubtless of mesenchymatous 

 origin. I was unable to find any trace of a tube lined by 

 primitive germ cells, such as was discovered by Hamann in 

 the young Asterias. 



What, we may finally ask, is the function of this strange 

 organ ? Cuenot, as usual, maintains that it is a lymphatic 

 organ. This I am disposed to doubt very strongly; the 

 cells which it contains are of quite a different nature from 

 the amoebocytes of the oral blood-ring, and the evidence that 



