60 THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
necessary to do more than refer to Moseley’s descriptions and figures. Von Kennel 
(8) could find no external circular muscle sheath in the forms examined by him, 
and I believe he has more or less misunderstood the entire arrangement ; it is, 
therefore, not necessary to discuss his observations on the subject. 
In the first instance, I propose to describe the different muscular systems in 
detail, following the arrangement proposed by Moseley in his admirable memoir 
already cited. (6) 
This author distinguishes between two principal systems of muscles, superficial 
and deep. Together with these he describes the special arrangement met with in 
the ‘‘ambulacral line” (where such exists), but the special muscles of the generative 
and digestive organs are described together with the other parts of these systems. 
The lateral muscular organs described by Moseley under the designation of 
‘“ambulacral lines’ do not exist in Geoplana travers nor in Geoplana spencert, and 
hence the arrangement of the muscular system is to some extent simplified. 
Superficial Muscular System.—This consists of two well-marked, perfectly distinct 
muscular coats, the only two really definite and distinct coats which it is possible to 
recognise throughout the body. The outermost lies immediately beneath the base- 
ment membrane of the epidermis, and forms but a very thin layer. This corresponds 
to and is homologous with the external circular layer of Moseley. It is composed of 
two distinct sets of muscles, and, as far as I can make out, only two. ‘The muscular 
bands of each set run approximately parallel to one another, but cross those of the 
other set obliquely, so as to leave a series of diamond-shaped interspaces (Fig. 19). 
This arrangement agrees precisely with that of the ‘‘decussating”’ fibres described and 
figured by Moseley (6) as occurring in the external circular layer. Moseley, however, 
states that some fibres take a directly transverse or circular course, a remark which 
I am unable to confirm in the case of Geoplana. He also observes that this layer of 
muscles is thickest in the dorsal region, and inferiorly on each side of the ambulacral 
line. In Geoplana spencer: it also seems to be somewhat thicker on the dorsal than on 
the ventral surface, but there is no great variation. Hach muscle band is made up— 
at any rate usually—of two or more delicate fibres. 
The inner of the two coats constituting the superficial muscular system is a 
layer of very well marked and strongly developed longitudinal muscles—the external 
longitudinal layer. This layer is rather more strongly developed on the ventral than 
on the dorsal surface of the animal, doubtless in relation to the crawling movements ; 
but the difference is not so great as described by Moseley (1) in the case of Geoplana 
traversit. tis composed of aseries of muscular bands, each made up of a number of 
separate fibres. These bands run, as a rule, approximately parallel to one another, but 
they not infrequently branch and anastomose, as represented in figure 19. ‘They are 
separated from one another by considerable intervals, about twice as wide as the 
