256 W. HAROLD LEIGH-SHARPE 
The spiral can be distinguished in a temporary preparation 
without resort to staining. 
The siphons arise in development (which will be dealt with in 
a succeeding memoir, since I am not yet sure as to the exact 
date of their definite appearance) apparently as invaginations 
of the ectoderm. The normal appearance of the body wall, for 
the purpose of comparison, is exhibited in figure 5. The epithe- 
lium is, of course, stratified. The tissues of the wall of the siphon 
A" 
Fig. 5 Scyllium canicula. Longitudinal section through the body wall. 
D.D., dermal denticles with p. c., pulp cavity, and e, enamel; Ep., epidermis; 
P.C., pigment cells; m., muscle; l.s., lymph spaces. 
are shown in figures 6 and 10... Here the epithelium is also strati- 
fied, and in the developing siphon (figs. 3 and 6) the band of 
muscle dorsal to the siphon should be noted. This is the muscle 
layer which exhibits such peculiarities mentioned later in the 
consideration of Raia. 
The siphon wall consists thus of: internally, a membrane 
comprised of a stratified epithelium; outside this a broad layer 
of circular muscles, imbedded in which, on the ventral side, is a 
band of longitudinal muscles, while, dorsolateral in position, is 
