COMPARATIVE STUDY OF SCOMBROID FLSHES. 
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The olfactory organs are a pair of grooves in front of the eyes. Each 
groove or sac communicates with the exterior by a pair of pores, nostrils. 
The anterior nostril is generally small, wliile the posterior is more or less 
elongated, oblong in the Cybiidae, and quite a slit in the Scombridae and 
Plecostei. Beneath the anterior nostril, there is a group of olfactory leaves, 
about 30 in number, arranged radially, in the form of a rosette. In the 
Scombridae two nostrils are situated rather near each other, and the upper 
wail of the olfactory cavity is uniformly thin. There is a deep groove in the 
floor of the cavity before the ethmoid, and just behind the olfactory rosette. 
The cavity extends behind the groove. The inner opening of the posterior 
nostril lies above the groove or before it. 
In the Cybiidae the olfactory cavity is rather small, and the two nostrils 
are close together, the whole cavity is nearly filled with the rosette of the 
olfactory leaves. In this family the posterior nostril lies more or less behind 
the rosette. The dorsal wall of the cavity is thin, but the border of the inner 
orifice of the posterior nostril is generali}' raised. Moreover the dorsal wall is 
tliickened in Sarda. Generally the cavity does not extend behind the posterior 
* 
nostril, and there is a fleshy dam behind the rosette and below the posterior 
nostril. 
In the Thunnidae there is a space behind the rosette, thus the two 
nostrils are much separated. The anterior nostril is very minute. The rosette 
of the olfactory leaves is high and occupies the whole height of the cavity. 
The dorsal wall of the cavity is very thick. 
In the Katsuwonidae the two nostrils are close together, and the cavity 
is much more depressed than in the Thunnidae. The passage of the anterior 
nostril is almost perpendicular to the surface of the head, wliile that of the 
posterior is more or less turned obliquely. The former lias the uniform calibre, 
but the latter is wide at the inner orifice, and becomes gradually naiTow towards 
the outer orifice. Between these nostrils there is a narrow groove on the roof 
of the olfactory cavity. 
ABDOMINAL CAVITY. 
In the Scombridae the height of the abdominal cavity is more than half 
the height of the body, and the cavity lies just beneath the vertebral column ; 
