On the tubuli in Devonian Lungfishes

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Abstract
Transverse sections of Chirodipterus australis and Griphognathus whitei are used to demonstrate the histological structures of the rostral and symphysial tubuli in Devonian lungfish. The walls of the tubuli are composed of bony tissue indistinguishable from the cancellar bone found in dermal bone. It has many spaces and perforations, and is contiguous in places with the cancellar bone of the external dermal bone. The walls of lateral-line canals have the same histological structure as the walls of the tubuli; they also intercommunicate with them. The tubuli and the lateral-line canals open to the surface through large perforations on the external surface. In Griphognathus the walls of the tubes under the external dermal bone have two layers: the outer one is dense bone, but the inner one has the appearance of calcified fibrous connective tissue of the kind associated with the tissue surrounding the lateral-line canals in living lungfish. The tubuli are closely related to the pore-canal system via canals that penetrate the dermal bone; this same relationship has been observed in Dipnorhynchus and Speonesydrion. The intimate connection between the tubuli and the lateral-line system suggests that they were formed by the sinking of neuromasts into and under the external dermal bone, with their walls surrounded by cancellar bone.