Points in the Histology of Celenterates. 257 
which I intend to give a brief provisional account in the 
following pages. I will first consider the Siphonophora. By 
employing a mixture of osmic and acetic acid, which agreed 
pretty closely with that adopted by the brothers Hertwig *, I 
succeeded in determining the presence of ganglion-cells in 
the feelers and pneumatophore of Apolemia uvaria and in the 
polypes 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 Meduse and other Ceelente- 
rates. In the same way the epithelium of the disk of 
Velella sptrans, as has already been described by Chun f and 
others, contains typical ganglion-cells. Sense-cells were 
found 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 different kinds, between which, however, tran- 
sitional forms occur. Forskalea 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 
Halistemma, 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 epithelio-muscle cells. Circular muscle-fibres are not 
found: at any rate the superficial prolongations of the epithe- 
lial cells, which run transversely and give a transversely 
rugose appearance to the stem, are not to be regarded as 
muscular, i 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 Ajpolemia, 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 Apolemia especially the development of 
the cells varies in a perfectly astounding way ; we find cells 
* QO, and R. Hertwig, ‘Das Nervensystem und die Sinnesorgane der 
Medusen,’ Leipzig, 1878. 
+ C. Chun, ‘Die Gewebe der Siphonophoren, II., Zool. Anzeiger, 
1882, no, 117. 
