230 s. GOTO. 



boundary between the disc and the preoral lobe as soon as the 

 force just mentioned comes into play. The only difference be- 

 tween the two species under consideration is that, in Asterias 

 pallida the portion of the plane of bilateral symmetry belong- 

 ing to the preoral lobe is very insignificant and can be neglected 

 for practical purposes, whereas in Ästerina gibbosa the preoral 

 lobe is still very large when it begins to be bent. It seems to 

 me that the number of cases where the plane of symmetry un- 

 dergoes secondary distortion is too mumerous to weaken the 

 explanation here offered. I therefore look upon my method of 

 orientation as still valid. 



I may add a word on the histology of the preoral lobe. 

 Previous observers have shown that the larvse are able to stick 

 to external objects by means of the preoral lobe, and MacBride 

 has published a figure ['96, pi. 27, fig. 136] of a section through 

 a larva sticking to an external object by means of a mass of 

 mucin ; but nobody has, so far as I know, shown where the 

 glands that secrete the mucin are, nor what their structure is. 

 I find in my sections that there are innumerable unicellular 

 glands not only in the "preoral pit" but also all over the an- 

 terior face of the preoral lobe, and especially concentrated along 

 its anterior margin. These cells are either goblet-shaped and 

 have long necks, or are simply tubular and more or less wind- 

 ing; their contents consist of granules which stain deeply with 

 Kleinenberg's hœmatoxylin and Bismarck brown, so deeply in- 

 deed that it is very difiicult to detect their nuclei. These cells 

 lie between the tall ectodermal cells of the preoral lobe, and 

 their openings on the surface of the cuticle are very distinctly 

 visible. It is needless to add that the granular contents give 

 rise to the mucin. 



