Sfractwre of HologUea dabi<i. 403 



Structure of liody Wall. One of the most striking features 

 is the entire absence of any cellular structure on the surface of 

 the body. When stained with Haenialuni or Picro-carmine, 

 transverse sections cut with the freezing microtome' showed, 

 except along the nuirginal lines, only a homogeneous jelly extend- 

 ing from the central cavity to the surface, without a trace of a 

 cell either in the jelly or on the external surface. Preparations 

 were made of four specimens, with precisely the same result 

 in each case. It is, of course, possible, but scarcely probable, 

 that every vestige of cellular structure, supposing such to have 

 once been present on the surface, may have been rubbed off. 

 The otherwise very definite and in all cases similar form and 

 appearance of tlie outside surface of the fourteen specimens 

 seem to indicate that this remarkable structure, or rather 

 absence of structure, is characteristic of the organism. 



As already said, the margins are very definitely modified. 

 Against a dark background they stand out white. In some cases 

 they are slightly broken and discontinuous, but as a general 

 rule they are regular. On the surface of each is a very definite 

 cuticular layer, sharply marked by reason of the fact that it 

 does not, or at most only slightly, take stain. On the oral pro- 

 jection, and also in some cases on the lower parts of the other 

 marginal lines and around the margins of the oral surface the 

 cuticle is distinctly serrated. (Figs. 5 and 5a.) Each serration 

 has a core of material that slightly takes stain. On either side 

 of the marginal lines the cuticle merges into the general outer 

 layer of the jelly, which sometimes has the appearance of being 

 slightly modified as if to form a thin cuticle over the jelly mass. 

 Heneath the cuticle of the marginal lines lies a band of very 

 finely punctated material, but beyond these punctations, which 

 are densest close beneath the cuticle, not a trace of structure 

 can be detected. There are no cilia, no ctenophoral plates, and 

 no canals. 



The terminal curved and serrated lip of one side of the groove 

 (Fig. 5) has the same structure as the marginal lines. 



The Central Canal. — The central tubular cavity, with the 

 aboral canal and certain structures associated with them, are 



1 I am in(lel)t.e(i to the kiminess of Mr. W. KieliliT for cuttiii",'^ these sections for me. 



