ACTINIARIA 



part of the body-wall in Edwardsia therefore differ in appearance from those of Isoedwardsia. In Edwardsia 

 we find in this region a thick ectoderm without cuticle (textfigs. 6, 62) and with scattered nematocysts; in 

 Isoedwardsia commonly, (but not always) a thin ectoderm, always provided with cuticle, and the nemato- 

 cysts enclosed in the nemathybomes (textfig. 69, compare below), The physa of the genus Edwardsia is 

 probably always perforated by apertures. It is true that I have not examined all the specimens of Edwardsia, 

 described here, in that respect, but as I have observed apertures in the physa of all the species (E. andresi, 

 vegae, arctica, finmarchica, vitrea, longicornis), the aboral end of which I have thoroughly examined, it may 

 not be precipitate to attribute such apertures to all Edwardsia-species. To judge from the structure of the wall 



Pig. 6. Fig. 7. Fig. 8. 



Textfig. 6. Longitudinal section of the proximal part of the body of Edwardsia andresi ne : nemathybomes, me : mesentery. 



The ectoderm of the physa is partly lost. Textfig. 7. Transverse section of the upper part of the actinopharynx with 



parts of the mesenteries of Edwardsia daparedii. Textfig. 8. A similar section in the lower part, si : siphonoglyphe. 



of the apertures of E. vegae it seems as if the apertures are invaginations of the ectoderm. The apertures 

 are surrounded by a circular thickening, possibly of the ectoderm and forming a movable stopping which is 

 directed outwards (textfigs. 50, 51) or inwards (textfig. 62), according to the different state of contraction of 

 the physa. The endodermal muscles form a circular sphincter round the apertures. The other Edwardsiidae 

 are probably devoid of aperture in the proximal end; I will, however, remark that I have not examined 

 the proximal part of the column as thoroughly as in the genus Edwardsia. 



The scapus is provided with a weaker or stronger cuticle or periderm. In Isoedwardsia ingolfi, and 

 Milne-edwardsia loveni I have found the strongest cuticle. In the genus Paraedwardsia there are "Halcampa- 

 papillae", which are wanting in the other genera. Concerning the structure of these papillae I refer to the 

 genus Halcampa. The nematocysts of the scapus-ectoderm in the four genera show a different arrangement 

 and are of a very different size, in comparison with the nematocysts of the capitulum. In the simplest case the 

 nematocysts of the scapus are scattered as in Paraedwardsia, now placed mainly on the ridges as in Milne- 

 edwardsia loveni, now for the greater part collected in larger or smaller clusters as in Milne-edwardsia carnea, 

 polaris and nathorstii. Sometimes these clusters are arranged in shallow invaginations of the mesogloea as 



