COMPARATIVE STUDY OF SCOMBROID FISHES. 
361 
in length with the rectum. The rectum is relatively long in Scomber too. 
Tire boundary between the small intestine and the rectum is indicated by a 
transverse ridge inside. In the so called scombroid fishes the length of the in¬ 
testine seems to have but little connection with the nature ef food, as voracious fishes 
of the Cybiidae have often a long iutestine, folded several times, and fishes of the 
Katsuwonidae, which feed on medium sized plankton, have a short, straight intes¬ 
tine. Rastrelliger which is a plankton-feeder has a very long intestine, more 
than 5 times as long as the length of the abdominal cavity. Usually the colour of 
the undigested ingredients of food differs in different tracts of the intestine. In the 
scombroid fishes the alimentary canal and genital and 
urinary ducts open to a common depression which is 
very shallow and communicates to the exterior with an 
elongated cleft. The anus, genital pore, and urinary 
pore all open independently on respective papillae. Of 
these the anus is the largest. The posterior wall of 
this cloaca-like space is more or less darker in colour 
tha n the anterior. When we handle the viscera of a 
tunny, more or less stale, with naked hands the wet 
portion becomes itchy, and in certain people the contact 
occasions small tumors of the skin. This is probably 
due to the formation of ptomain. In the viscera of a stale fish we often find 
small crystals on the external surface of the mass of the pyloric coeca. 
Liver (figs. 2, 3, 5, 6). The liver is a large brownish organ, generally 
divided into three lobes, and situated just behind the diaphragm, and covers 
the anterior and ventral part of the stomach. In the Scombridae the live, 
differs remarkably in form from the other allied fishes. It is a small, undividedr 
more or less triangularly pyramidal organ, with three trenchant edges. It is 
situated at the left, anterior corner of the abdominal cavity. The right hepatic 
vein is found at the attenuated margin of the right, anterior corner. The 
middle and right lobes are scarcely developed. In the Cybiidae we find three 
lobes of the liver, but their respective size and form are variable. Generally 
the right lobe which is scarcely developed in the Scombridae, is best deve¬ 
loped, but the left and middle lobes are poorly developed. In Gi/mnosarda, 
however, the left lobe is best developed. 
1, Scomber japonicus 
2, Neothunnus macropterus 
Fig. M. External aper¬ 
ture of the cloacal cavity 
(enlarged), showing from 
above the anal, genital, and 
urinary openings on the 
respective papilla. 
