Points in the flistoJogy of Ccelenteratefi. 257 



wliicli 1 intend to give a brief ])vovisional account in the 

 following pages. I will first consider tlie Siplionophora. By 

 employing a mixture of 08inic and acetic acid, which agreed 

 pretty closely with that adopted by the brothers Ilertwig *, I 

 succeeded in determining the presence of ganglion-cells in 

 the feelers and pneuniatojihore of Apolemia uvaria and in the 

 ])olypes of Forskalea contorta^ which in the form of the cell 

 and its prolongations do not differ from those with which we 

 are acquainted in the case of the Medusfe and other Coelente- 

 rates. In the same way the epithelium of the disk of 

 VeUUa spiralis, as has already been described by Chunf and 

 others, contains typical ganglion-cells. Sense-cells were 

 ibund at the anterior extremity of the polypes and feelers of 

 Apolemia, likewise in accordance with the well-known 

 arrangement. On the other hand, the stem of the two Physo- 

 phorids alluded to contains highly remarkable and divergent 

 cellular structures. In this case the epithelium consists of 

 cells of very difi'erent kinds, betw^een which, however, tran- 

 sitional forms occur. ForsTcalea exhibits on the sides of the 

 stem transversely elongated cells, which send off a process 

 into the interior, and by means of this, which may again 

 divide, they are connected with the longitudinal muscles. 

 Another Physophorid, which I determined to be a young 

 Ualistenwia, in the stem of which the central canal is extra- 

 ordinarily wide while the septal ridges of the supporting 

 lamella are very low, exhibited these conditions particularly 

 clearly ; it follows from this that in the stem we have to deal 

 with e{-ithelio-muscle cells. Circular muscle-fibres are not 

 found : at any rate the superficial prolongations of the epithe- 

 lial cells, Avhieh run transversely and give a transversely 

 rugose appearance to the stem, are not to be regarded as 

 muscular, in spite of their fineness, length, and often very 

 homogeneous appearance, as I shall show in my detailed 

 paper. Their superficial position is also an argument to the 

 contrary. In Ajwlemia, however, we find muscle-substance 

 enclosed in these prolongations of the body of the cell and 

 likewise in the central processes which lead to the longitu- 

 dinal muscle ; nevertheless this is not the case for all cells of 

 the epithelium, although it is not thereby possible to divide 

 the epithelial cells into those which contain muscle and those 

 which do not. In A^joleiyn'a especially the development of 

 the cells varies in a perfectly astounding way ; we find cells 



* O. and E. Hertwig, * Das Nervensjstem und die Sinnesorgane der 

 Medusen,' Leipzig, 1878. 



+ C. Cluin, * Die Gewebe der Siphonophoren. II.,' Zool. Anzeiger, 

 1882, no. 117. 



