MONOGRArn OF JAPANESE OPHIUROIDEA. 



55 



by a row of plates, supporting and protecting the cavity «in which 

 the generative glands lie. In the sterile parts of the arms, these 

 plates are replaced by two rows of nodules in each joint in 

 Astroceras, and by two rows of minute scales in Asteroschema. In 

 Trichaster, there are four pairs of generative glands in each arm, 

 which bears masses of irregular nodules. These nodules are ar- 

 ranged in two la}T'rs and form three or four rows on either side 

 of each joint in the proximal parts of the arms : two of the rows 

 belonging to the internal layer, two to the external layer on the 

 ventral side and one on the lateral side. Besides, there is a large 

 nodule on the upper end of the ridge formed by the rows of 

 nodules on either side of each joint. These nodules form two 

 longitudinal rows of humps on each arm. In the sterile part of 

 the arms, the nodules are replaced by two rows of scales in each 

 joint. The species in which the extension of the generative glands 

 into the arms has been observed are shown below, together with 

 some additional facts. 



