322 MR. E. W. SHANN ON THE 
Here we have an exposition of the two-layer theory of the 
lateral muscle of Teleostei, differing in few points from that 
advanced by Humphry. 
Wiedersheim (9) describes the completeness of the division of 
the dorsal and lateral moieties of the lateral muscle by a con- 
nective tissue septum extending from the axial skeleton to the 
integument at the region of the lateral line. Only one layer of 
muscle is recognised. 
With Knauer (5) we are brought into contact with a new view 
of the lateral muscle. It is divided longitudinally into two main 
portions which are defined according as they arise from (@) the 
head (Riickenmuskulatur) or (6) the neck (Bauchmuskulatur). 
The division at the lateral line, though complete, is only regarded 
as being of secondary importance. The oblique line in the table 
severing the back musculature from the belly musculature indi- 
cates the author’s contention that the former gradually pushes 
its way over the latter as we proceed in an antero-posterior 
direction. Finally, in the posterior abdominal region the back 
musculature comes completely to enclose the diminishing belly 
musculature ; and in this area a true stratification of the body- 
wall is realized. His lateral line muscle is syronymous beyond 
doubt with the “ red fibres ” of other authors. 
Text-figure 1. 
A 
Diagram to illustrate the apparent (ABCDE) and the real (ABHC’H’Dk) 
construction of a myomere. (After R. Chevrel.) 
Dietz (2) bases his division of a Teleostean myomere, and hence 
of the lateral muscle, on the transverse septum extending beneath 
the lateral line. His subsequent divisions are due to the direc- 
tion of the myocommata. He proceeds to investigate myomeres 
from various parts of the body, and shows how the pleuro-dorsal 
portion gradually becomes emancipated from the pleuro-ventral 
as we proceed antero-posteriorly; with this is correlated the 
