381 
o f Edinburgh , Session 1876-77. 
of the nerve-area. Externally are circular coat, hypoderm, and 
cuticle. Posteriorly the cords are connate, and a single neural 
canal of considerable size exists superiorly. 
Serpulule. — In Protula protensa the cords anteriorly are situated 
under the great longitudinal dorsal muscles as widely separated 
trunks. They then fall into position and approach the increasing 
longitudinal ventral muscles — a large neural canal being at the 
inner border. Posteriorly the neural canal is proportionally larger 
than in front, but the relations of the nerves are similar. At their 
commencement in front the nerve-cords are internal, and have 
beneath them all the tissues under the dorsal muscles. After 
reaching the inner border of the ventral longitudinal muscles they 
have externally ( i.e ., interiorly) a thin layer of longitudinal mus- 
cular fibres, the circular coat, hypoderm, and cuticle. A transverse 
band bounds them superiorly. Posteriorly the first-mentioned 
(longitudinal) layer is absent externally. In Serpula vermicular is, 
L., a similar arrangement occurs, but the neural canal is external, 
that is, next the ventral longitudinal muscle, and the thin longi- 
tudinal stratum is internal. 
4. On the Application of Graphic Methods to the Deter- 
mination of the Efficiency of Machinery. By Professor 
Eleeming Jenkin. 
{Abstract.) 
The general scope of the paper was to show how by graphic 
methods we might find the relation between effort exerted at one 
part of a machine and the resistance overcome at another part. 
It was shown that for a given machine at any instant a linear 
frame might be substituted, such that the stresses in the links 
corresponded to the pressures at the joints between the elements 
of the machine, including the pressures due to driving effort and 
resistance. Numerous examples were given of the application 
of this frame, called the dynamic frame, to the solution of the 
above problem, the friction, inertia, and weight of all the parts 
being taken rigidly into account. 
