The Anatomy of Chlamydoselachus 



455 



both are decidedly variable. That they are not essential for the life of the fish is indicated 

 by Hawkes' observation of an adult female with both abdominal pores closed. 



PERICARDIO'PERITONEAL CANALS 



In the embryonic development of higher vertebrates, the primitive coelomic cavity 

 becomes divided into three cavities, pericardial, pleural and peritoneal respectively. In 

 the adult elasmobranch there are only two coelomic cavities, pericardial and peritoneal, 

 and their separation is not quite complete. A pair of slender thin-walled canals, joined 



Text'figure 99. 

 Diagrams showing the pericardio'peritoneal canals (dorsal views) in: A, an 

 adult Squalus; and B, an adult ScylUum. Dorsal parts removed by a hori- 

 zontal cut. The canals below the esophagus are represented by dotted lines. 



dcv, ductus Cuvieri; dm, dorsal mesentery; !ig, lateral suspensory ligament of !, the liver; lo.ro, 

 left and right openings of the pericardio-peritoneal canals; oe, esophagus; p, pericardial coelom; 

 po, median opening of the pericardio-peritoneal canal into the pericardial coelom; rlig, right 

 lateral suspensory fold; sm, sub-esophageal lesser mesentery (hepato-enteric mesentery). 

 After Goodrich, 1918.1, Fig. 18. 



at their pericardial ends to form a single large canal opening into the pericardial cavity 

 (Text 'fig. 99), course posteriorly along the ventral wall of the esophagus to open by wide 

 apertures, thus placing the pericardial cavity in communication with the peritoneal 

 cavity — as in Squalus and Scyllium (Goodrich, 1918.1, Fig. 18); and Raja (Monro, 1785). 



Pericardio-peritoneal canals of selachians were first described and figured by Monro 

 in the skate. Balfour (1876-78) interpreted these canals as developmental arrests, but 

 Hochstetter (1900) claimed that in Acanthias the early communication between the 

 pericardial and peritoneal cavities became completely closed, and that the canal opening 

 from one to the other in the adult is a new formation. Goodrich (1918.1) investigated 

 the development of these canals not only in Squalus (Acanthias) but also in Scyllium, 

 concluding that Hochstetter was mistaken in his interpretation and that Balfour's 

 view is essentially correct. 



In each of my four large specimens of Chlamydoselachus, pericardio-peritoneal 

 canals were found. Since there is considerable variation in the structure and relations 

 of these canals, each specimen will be described separately. 



