CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 503 
authors say. 1 Moreover, there is nothing in these appendages 
which recalls to mind the internal glandular mass of the cones 
of Clione. 
Structure of the Suckers. 
The only histological knowledge of these organs which we 
formerly possessed proceeds from Gegenbaur’s researches, 
who attributes a very simple structure to them. 2 But this 
knowledge was not very extensive. 
During the month of January, 1885, I studied the structure 
of these suckers by means of a series of transversal sections. 
I had scarcely finished this study when I received the thesis of 
Niemiec, “ Recherches morphologiques sur les ventouses dans le 
regne animal.’’ 3 In this work the structure of the suckers of 
Pneumodermon is carefully described and represented. My 
own observations agreeing almost entirely with those of the 
Swiss zoologist, I believe it useless to explain them at length. 
Hence I refer to the memoir of Niemiec, limiting myself to 
the principal points relative to the structure of the sucker and 
to indicating a few points of detail in which I do not entirely 
agree with the Swiss zoologist. 
The body of the sucker is formed of a layer of large, pris- 
matic, muscular cells (figs. 24 and 25), the contents of which 
are formed of different separated fasciculi of fibres (a). These 
fasciculi have the form of very flat, three-sided prisms, of 
which the most acute angle is turned towards the centre of 
the cell. In this place we find the nucleus (6), which has a 
shape analogous to that presented by the nucleus of the mus- 
cular cells of the cones of Clione. All around, towards the 
upper side of the disc formed by this layer of prismatic cells, 
we find a sphincter formed of not very numerous annular mus- 
cular fibres. The upper face of the muscular disc is covered 
with a pavimentous epithelium (fig. 23, c) with excessively flat- 
tened cells, whose nucleus is consequently excessively flat. 
1 Claus, ‘ Handbuch der Zoologie,’ French translation, p. 1056. 
2 Gegenbaur, loc. cit., p. 77. 
3 ‘ Recueil zoologique suisse,’ t. ii, 1885. 
