INFLUENCE OF LATERAL-LINE CANALS 325 
MeMurrich (’84, p. 279) gives a more elaborate account of 
the nature of the head skeleton of Amiurus, but agreeing with 
the above conclusions. He, too, based his statements on a 20- 
mm. larva of Amiurus which he had studied histologically. 
The bone which first appears in the head is the supraoccipi- 
tal, which with its heavy spina occipitis is a very evident ele- 
ment in the cleared specimen at this stage. It is clear that its 
origin is in no way involved in the latero-sensory canals, the 
plan of which is already laid down as shown by the photograph 
(fig. 2) in direct sunlight under a binocular of a specimen 24.2 
mm. long. The sphenoties arise in relation with the lateral- 
line system and are in a definite way influenced by it. Thus 
tophicity of the lateral-line system for this particular bone is 
suggested. The impulse which initiates the development of the 
skull bones is a deep-seated factor in determining the time of 
origin of many of the osseous elements. 
Fig. 2 Photograph of a dorsal view of the anterior part of body of a young 
Amiurus (24.2 mm., measured from tip of caudal fin), showing the nature and de- 
gree of ossification of the skeleton of the head and girdle. The ossification, 
segmental in nature, along the supraorbital lateral-line canal is especially note- 
worthy. 
ABBREVIATIONS 
a.d.f.s., anterior dorsal fin spine post.font., posterior fontanelle 
b., barbel r. 1., greatly expanded first parapo- 
b.o., ossification in base of barbel physis 
d. f. s. posterior dorsal fin spine r. 2., rib, of second vertebra 
ect., ectethmoid r.3., rib, of third vertebra 
fr., frontal, ossification of the trans- — scl., supraclavicle 
verse bar soc., Supra-occipital 
f.s., fin spine of pectoral fin Sp. 0c., Spina occipitis 
g. b., clavicle forming girdle base 
hmb., hyomandibular 
l.l.c., right lateral-line canal 
m., mandible 
n.a., nasal 
orb., orbit 
ot., otolith 
p.r.1.,posterior expansion of first para- 
pophysis 
psf., postfrontal 
pst., posttemporal 
sp. ¢., supra-orbital lateral-line canal 
st., subtemporal lateral-line canal 
continuous with mandibular canal 
st. ¢., supratemporal lateral-line canal 
ts. transscapula 
v. 2., second vertebra 
x., posterior expansion of supraorbital 
canal. 
x’., point of influence of lateral-line 
eanal on primary ossification of 
frontal bone 
