262 E. RAY LANKESTER, ON THE 
MuscutarR systeM.—The various modifications of the 
muscular layer of the integument constitute the principal 
part of the muscular system in the earthworm. There are but 
few special developments of muscular tissue in such organisms 
at all; the various functions which are entailed on ” special 
muscles in higher animals being here performed by a simple 
contractile tunic or membrane. The muscular coat succeeding 
the pigmentary layer of the integument (the cutis being 
inseparable, and not easily distinguished from those struc- 
tures) consist of fibres which run. transversely to the longi- 
tudinal axis of the body, and by their contractions cause the 
rings to diminish their diameter ; the succeeding layer to 
this is formed of intercrossing and oblique fibres, whilst the 
innermost fibres are arranged longitudinally. These last 
are by far the most numerous, and are largely developed on 
the ventral surface. They form the straight muscles of 
Morren. ‘Two lateral muscles, a ventral, and a dorsal, may 
be distinguished (fig. 11). The setigerous glands occupy 
a position between the dorsal and lateral and the lateral and 
ventral muscles on either side. Morren has carefully de- 
scribed an arrangement of minute muscular fibres in connec- 
tion with the setz, which he considers as the protractors and 
retractors of these appendages. Cuvier has also described 
these. 
The object of the muscular attachment appears to be 
to keep the seta in position rather than to withdraw or 
extend it, so that the hooklet may yield to pressure from the 
quarter towards which the worm is progressing, but offer 
resistance to similar force in the opposite direction. The 
remaining muscles of the earthworm are the transverse or 
intraseptal muscles, or modifications of these. Between 
every segment or ring a very delicate, tenacious, pellucid, 
muscular membrane exists, loosely connected with the 
internal viscera, but firmly attached to the walls of the 
body. These transverse muscles do not entirely close the 
various rings from each other, but allow the contents of 
the perivisceral cavity free movement from one end of the 
body to the other. The fibres of the transverse muscles are 
very fine, and take a direction from the walls of the 
splanchnic cavity towards the central viscera. In the first 
eight or nine rings of the body oblique radiating muscular 
fibres diverge from the transverse muscles, and become 
attached to the muscular pharynx to be described hereafter. 
A somewhat similar arrangement occurs in the terminal 
rings of the body, where these radiating fibres assist in the 
expulsion of the feeces from the anal aperture. 
