No. 2.] MORPHOLOGY OF THE ACT/NOZOA. 14I 



matozoa ; but this, so far as I know, never occurs in any of the 

 Hexactinians. I believe, therefore, that C. Americanus is really 

 bisexual, and not dichogamous. 



3. Histology. 



The maceration of fresh tissues gives the most satisfactory 

 results as to the structure of the histological elements in the 

 Actiniaria. This method I was unable to employ, and the 

 maceration of preserved specimens gave as usual unsatisfactory 

 results. Nearly all the facts I have to present have been 

 derived from the study of sections, and are therefore somewhat 

 fragmentary. They suffice, however, to show a very close 

 similarity in the histology of C. Americamcs to that of C. ment- 

 branaceus, as described by the Hertwigs ('79), von Heider ('79), 

 and Jourdan ('80), and, on the other hand, considerable differ- 

 ences from what Danielssen ('89) has described for C. borealis, 

 Danl. 



(a) Te7itacles and Disc. 



The ectoderm in these parts is covered by a very distinct 

 cuticle, which shows a dotted appearance, produced probably 

 by the existence of perforations for the passage of the cilia. 

 The outer portion contains numerous nematocysts which stain 

 deeply with borax-carmine and are cylindrical or slightly curved 

 with the filament spirally coiled. They resemble those de- 

 scribed by von Heider and Haime in the same situations. Two 

 kinds of gland cells are present ; one resembles goblet cells, and 

 are by far the most abundant, the other kind occurring only 

 sparingly, and being of the structure figured by the Hertwigs 

 (PI. Vni., Fig. 15, d) and by Jourdan (PI. XH., Fig. 85,^). I 

 could not observe that the latter kind were more numerous in 

 the oral tentacles than in the marginal as Jourdan describes, the 

 histological structure of both series of tentacles being identical. 

 In the disc, however, they do seem to be more abundant than 

 in the tentacles. In sections which were slightly torn I could 

 perceive indications of the presence of " Stiitzzellen " and sen- 

 sory cells, but maceration preparations are necessary for their 

 proper study. 



Below the epithelial layer to which these structures belong 

 comes the nerve layer. In the tentacles the nerve fibrils are 



