28 
the combined action of the muscles and the fluid distending the 
tissues, this lip-fold is more or less protrusible. Another argument 
for this supposition may perhaps be found in the numerous trans- 
verse wrinkles which were observed in the cellular coating of 
the pharynx. 
Between the external mouth and the fold # there is another set 
of folds, which are very regularly placed and must be more eir- 
cumstantially described. They are represented in transverse section 
in fig. 17, their real nature can however only be made out by 
combination of these with horizontal and longitudinal sections. It 
is then evident that only the lipfold t and the fold ?, situated di- 
rectly under it, are circular, and indeed surround the mouth on 
all sides, whereas the folds b, b' and p are semicircular or horse- 
shoeshaped, only encircling the anterior portion of the mouth-ca- 
vity. The two folds b and b’ are covered for the greater part by 
a strongly eiliated epithelium, muscular fibres, with blood-lacunae 
between them, playing a prominent part in their structure. The 
epithelium consists of high columnar cells with very distinct nucleus, 
the cilia are long. | 
The fold p between them is not a fold in the striet sense be- 
cause it is constituted by numerous tubular outgrowths of the epi- 
thelium of the mouth cavity. Figure 29, p, represents their ar- 
rangement in a horizontal section just above the mouth. These tubu- 
lar structures have a hollow canal inside and are comparatively so 
thin that only one layer of colummar epithelium cells sustained upon a 
delicate membrane forms the walls. Exteriorly these cells are co- 
vered by a thin cuticle; at all events not ciliated. "The tubercle 
being apparently hollow, the question arises whether blood may 
penetrate into them and eventually undergo a respiratory process, 
thanks to the easy access of fresh seawater. Their strong histolo- 
gical resemblance in certain respects with the branchiae of Neomenia 
(as a comparison with Prof. Ray LANkESTER’s and v. GRAFF’S sec- 
tions showed) affords another hint in this direction. An important 
difference however is this that the latter are situated, not just in- 
side of the mouth, but in the anal cavity. Moreover I could not 
