ASTERIAS PALLIDA. 247 



from near the centre of the oral side. In stage E the aboral disc is 



inclined at an angle of about 45° to the sagittal plane, and in F it is 



nt right angles to it. It has here assumed its final position and from 



now onward the pra?or;d lobe has only to shrink in for the star to be 



complete. It may be stated in addition that the prgeoral lobe is, just 



before its final disappearance, situated on the right side of the oral 

 disc. 



As stated above, the aboral disc grows, in its later stages, largely by 

 a chano-e of form of the cells of the surroundino" reofion. This means 

 that the shrinkage of the prœoral lobe and the portion adjoining the 

 mouth is due to the same cause. So far as I have observed, the thickened 

 patches between the arms of the brachiolaria and their thickened tips 

 are the only parts that undergo histolysis. AVhile the general ecto- 

 derm stains blue with ha^matoxylin, these patches show, after stage F, 

 a decidedly reddish tinge, and numerous amœbocytes are observed in 

 their vicinity. 



As to the nature of the thickened patches between the brachiolar 

 arms I can not say anything positive. In Asten'na (jihbosa MacBride 

 has observed in a corresponding position a glandular patch, by which 

 the larva attaches itself very effectively to external objects while it is 

 undergoing metamorphosis ; Bury also states that " metamorphosis is 

 ushered in, in the larva oï Ast er las ruhens, by the fixation of the larva 

 by the knobbed arms of the brachiolaria, and the ciliated pit which 

 they surround" ['95, p. 74]. In view of these facts as well as of the 

 general appearance of these patches which look suspiciously glandular, 

 I have tried Bismarck brown ; but whether from some fault in the 

 brown^^ I used, or owing to a real absence of glandular cells, I have 

 not succeeded in obtaining a differential stain. The latter alternative 

 appears to me more probable, as the brachiolaria or transforming larva 



1). It is stated to have come from J. D. Riedel, Berlin. 



