THE SENSORY CANAL SYSTEM OF FISHES. 519 
tive pores, &c., on the sides of the head and gill-flap in 
Polyodon. 
The Glossopharyngeal.—Ewart has suggested that 
possibly the most anterior portion of the lateral canal may be 
innervated by nerve-fibres from the glossopharyngeal nerve 
previous to its leaving the cranial cavity, but so far he has 
failed in Lemargus to find any branches which pass to either 
the sensory or ampullary canals from this nerve. In Polyodon 
I have met with similar results, the anterior portion of the 
lateral canal being innervated by the branch /’. (Pl. 40, fig. 11) 
of the vagus. This branch also innervates the cluster pores in 
the occipital region. 
The Vagus.—The lateral division of the vagus supplies the 
lateral canal and its associated organs. It gives off a number 
of branches all along its course, which innervate the branches, 
cluster pores, and other sensory organs situated in the region 
of the canal. 
Vill. PSEPHERUS GLADIUS. 
The sensory canal system of Psepherus approaches very 
closely to that described in Polyodon, to which it holds the 
same relation as Calamoichthys does to Polypterus. 
From an external examination of specimens in the British 
Museum little or no difference could be observed in the form 
and distribution of the canal and its branches. 
I have described in Polyodon a series of sensory organs in 
the region of the lateral canal which I am inclined to regard 
as modified cluster pores, and synonymous with the ‘ spalt- 
papillen” of Fritsch. In Psepherus these are rather larger 
and more numerous. 
A partial dissection of the head of a small specimen was 
made, in which the dermal portions of the main canal and its 
branches were all found to agree with the condition present 
in Polyodon. 
In the smallest specimens examined there were no cluster or 
primitive pores visible on the lateral canal, and no trace of 
branching. Ina specimen about 320 mm. long the branches 
seemed to be in a very early stage of formation. 
