BULLETIN OF THE UNITED STxI.TES FISH COMMISSION. 
/. Circular layer. 
g. Kuilimeutary male generative organs. 
/i. Kndimentary female generative organs. 
i. Position of genital aperture. 
к. Subcuticular granular layer, vitellaria. 
Fig. 2. Diholhrium cordicaps. Transverse section near anterior end. X 75. 
aaa. Peripheral aquiferous vessels. 
hh. Central aquiferous vessels 
CO. Marginal canals. 
d. Kow of nuclei connecting marginal canals, 
ee. Bothria. 
/. Epidermal layer. 
g. Nerve cells ? 
Fig. 3. Longitudinal section near margin. (The outer layer of longitudinal muscles is wanting near 
the margins, the space being occupied by masses of nuclei which have much the same ap- 
pearance in longitudinal sections as they have in transverse sections.) X about 250 
diameters. 
a. Cuticle. 
1). Subcuticular granulo-nuclear layer. 
CO. Periiiheral aquiferous vessels. 
d. Calcareous body, showing concentric structure. 
e. Longitudinal muscle layer. 
/. Nuclei of vascular layer. 
Fig. 4. Calcareous body, optical section showing concentric structure, x about 750 diameters. 
Fig. 5. Portion of abdominal wall of Salmo miikiss with parasite inclosed. X 3. 
a. Epidermis of host. 
b. Muscular tissue of host. 
c. Connective tissue layer of cavity in which the parasite lies. 
d. Posterior end of parasite. 
e. Anterior end of same. 
Drawings by the author. 
EXPLANATION OF PLATE XXVI. 
Fig. 1. Bihothrium cordiceps, anterior cud. 
Fig. 2. Middle. 
Fig. 3. Posterior end. Figs. 1-3, X 6. 
Fig. 4. Transverse section of longitudinal vessels, near anterior end. X about 200 diameters. 
аа. Cut end of longitudinal muscles. 
bb. Circular muscles. 
cc. Calcareous bodies. 
c'c'. Same in optical section, showing concentric structure. 
d. Marginal canal. 
e. Central aquiferous vessel. 
Fig. 5. Longitudinal section of pulsatile vessel posterior end. X about 200 diameters. 
a. Layer of columnar epithelium. 
b. Excretory pore. ^ 
c. Cuticle. 
d. Subcuticular layer of nuclei. 
e. Parenchyma with connective tissue and nuclei. 
/. Nuclei of muscular layer surrounding pulsatile vessel. 
/'. Granulo-nuclear layer sup[)ortiug columnar epithelial layer. 
gg. Longitudinal muscle fibers. 
h. Cluster of nuclei marking lirst appearance of second pulsatile vessel. 
Drawings by the author. 
