62 ; THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
Jijima, in his very important work on the fresh-water Tricladians, already 
referred to, distinguishes between ‘‘ Hautmuskulatur’’ and ‘‘ Korpermuskulatur.”’ 
In the first he includes the different layers of muscles lying beneath the skin at the 
periphery of the body, and in the second the dorso-ventral and transverse muscles. 
The homologues of the two constituents of the ‘‘Kérpermuskulatur” are evidently to 
be found in the dorso-ventral (or bolting) and transverse (or supra-neural) muscles of 
Geoplana. The question arises, ‘‘Is the superficial muscular system of Moseley the 
equivalent of the ‘‘ Hautmuskulatur’’ of Jijima, or does the latter include also the 
longitudinal and more or less circular fibres of Moseley’s deep system?” According 
to my view of the case the ‘‘ Hautmuskulatur ” of Jijima is the equivalent of the 
superficial muscular system of Moseley, and the longitudinal and more or less circular 
fibres of Moseley’s deep system are an extra development, either wanting or poorly | 
developed, and not yet recognised in the fresh-water forms. An examination of 
Jijima’s figures 3 and 4 (Taf. xx.), and comparison of the same with my own figures, 
seem to me to establish the truth of this view. It will be seen from these figures 
that the whole of the ‘“‘ Hautmuskulatur” im Planaria polychroa forms a thin layer 
lying immediately beneath the basement membrane of the epidermis, and occupying 
a thickness much less than that of the epidermis itself. Moreover, Jijima’s figures 
show it lying entirely outside the special zone of rod-like bodies and the nerve sheath, 
exactly as is the case in Geoflana. In short, the internal longitudinal muscles of 
Planaria polychroa, which form the deepest layer of the ‘ Hautmuskulatur,” 
correspond precisely in position to the external longitudinal muscles of Geoplana and 
other land Planarians, and the two layers are, I believe, homologous. 
This longitudinal layer of muscles appears to be constant in both terrestrial and 
fresh-water Tricladians, while all the other layers are subject to more or less 
variation in the different forms. This constancy of the one layer only appears to me 
to indicate that this layer alone is homologous throughout the terrestrial and fresh- 
water Tvicladians. 
Jijima gives the following tabular scheme of the arrangement of the muscle 
layers in the forms examined by him :— 
Planaria polychroa. Dendrocoelum lacteum. Polycelis tenuis. 
Circular fibres. Circular fibres. Circular fibres. 
Superficial System. External longitudinal fibres. —. External longitudinal fibres. 
(Hautmuskulatur.) 
Oblique fibres. Oblique fibres. =e 
Internal longitudinal fibres. | Longitudinal fibres. Longitudinal fibres. 
Deep System. Transverse fibres. Transverse fibres. 
(Korpermuskulatur.) 
Dorso-ventral fibres. Dorso-ventral fibres. Dorso-ventral fibres. 
