Hyatt,] 132 [March 5, 



were constantly under observation for several months, nearly all 

 possible outlines were seen in different parts of the ectoderm ; 

 but they remained always angular and flat, or if swollen were 

 barely convex and did not present the globular expansions of the 

 outer surface once seen in the cells of the endoderm. The ordin- 

 ary shape was fusiform, and usually the interior was clouded more 

 or less with granules collected in two crescents around the poles 

 of the nucleus. In this resjDect, however, there was no invaria- 

 bility since we have seen unquestionable ectoderm cells absolutely 

 filled with highly ref ractile granules ; but the nucleus on account of 

 the flattened form of the cells was never obscured. Keller's draw- 

 ings exhibit the usual aspect of the ectoderm in dead specimens, 

 but they are not in all cases so clear in the living, especially in the 

 vicinity of the nuclei. Metschnikoff (Quart. Journ. Micr. Sci. 

 Jan. 1874, translation) declares his opinion, derived from exper- 

 iments with Ascetta primordialis and the embryo of Halisarca 

 lobularis, that the ectoderm is not instrumental in the ingestion of 

 food ; and (though Von Lendefeld entertains doubts on this point 

 as we have quoted below), most observations appear to sustain this 

 conclusion. 



The cells of the ampullae had the usual form, but my drawings 

 give no observations of value, except that in living specimens I 

 never saw any accumulations of an excretory nature in the 

 ampullaceous chambers. The cells contained also an abundance 

 of refractile granules. 



The cells of the derm (Sci. Guide, no. in, f. 2, 14-18) varied 

 from transparent and flattened, with fusiform outlines in Chal. 

 arbuscula, to opaque cells distended with highly refractile gran- 

 ules. The former were constantly contracting and expanding 

 without, however, leaving their places in the derm, and they lost 

 their usually fusiform outline only in extreme cases when form- 

 ing part of some thread-like extension across a tube. 1 In one 

 specimen some of these cells around a narrow tube were elongate- 



1 These were the only cells found which could be described as possible muscular ele- 

 ments; but as in all others examined by us in the mesoderm they were capable of 

 slowly but constantly changing their forms, and seemed to possess considerable pow- 

 ers of adhesion to each other as if connected by bands. The nuclei were never modi- 

 fied, but remained rigid causing the centres of elongated cells to stand out in minute 

 prominences. There were no grounds for the supposition that these or others observed 

 were muscular cells. 



