326 ROY L. MOODIE 
Suggested explanations for this are given later on. The lateral 
peripheral osseous elements appear much later than the supra- 
occipital and especially is this true of the suborbital chain of 
bones, to the development of which the lateral-line system is so 
intimately related. Our knowledge of the nerves and sense 
organs of the lateral-line system of Amiurus is adequate, the 
subject having been discussed by Wright (’84) and Herrick 
(01) and further developed in other siluroids by Allis (04). 
CONDITION OF THE HEAD SKELETON OF AMIURUS AT 24 MM. 
Returning now to a consideration of the bones of the head in 
their relation to the lateral-line canals in Amiurus, reference may 
be made to figure 11 in Kindred’s (19) paper to show this asso- 
ciation. He figures an advanced stage after the formation of 
both sets of bones. As I have previously stated, the set least 
associated with the lateral-line system is the first to develop. 
The distinctness of the supra-occipital from the lateral-line bones 
is indicated by Kindred’s (’19) statement: ‘‘ There is no lateral 
line ossification anywhere near the vicinity of the developing 
supra-occipital.’”’ This is shown in figure 2. The supra-occipital 
later grows out in contact with the lateral-line canal and is modi- 
fied by it. MceMurrich (’84, p. 271) states, “it (the supra-occip- 
ital) presents (in the adult) many minute foramina, belonging 
to the system of the mucus canals.” 
The first bones in the head may develop in response to stress, 
for they are seen (fig. 2) in the occipital region at the point where 
the head joins the body. The first vertebra with its large para- 
pophysis (fig. 2, 7.1.) is extensively ossified, as are likewise the 
dorsal spines. The elements of the pectoral girdle are also easily 
identified, though they have not all developed equally. The 
great advance in ossification shown by the frontal is difficult to 
understand, since it is not subjected to strain and only in part 
to the direct influence of the lateral-line system. All other dor- 
sal cranial elements except the supra-ethmoid and all lateral 
ones with the exception of the hyomandibular are developed 
in response to some influence exerted by the lateral-line canals. 
