34
F. B. SHORLAND
aquatic animals. However, this situation may arise from differences in
the dietary fat rather than from inherent differences between species.
1. Fats of Invertebrates
Hilditch (3) refers to the fatty acid composition of the depot fats of
six insects of the Orthoptera, the chrysalis oil of the silkworm and
the tent moth, as well as the larva fats of a few other groups. The composition of insect fats is variable. The saturated acids comprise 15-35%,
with palmitic acid as the main component. In accord perhaps with the
green-leaf diet, the unsaturated acids are mainly Ci 8 with linoleic and
linolenic acids often predominating. C 20 and C 22 unsaturated acids
appear to be generally absent but have been reported in substantial
amounts (26-44%) in the depot fats of two Mexican species (174, 175)
including the Mexican locust. The fatty acids from the latter, however,
failed to give the polybromide test for C 20 and C 22 highly unsaturated
acids. The fatty acids from the other Mexican insect gave ether-insoluble bromides which darkened at 200°. The evidence for the presence of polyunsaturated C 20 and C 22 acids in these insects is thus rather
inconclusive. The effect of the dietary fat is evident on comparing the
larva fats of the beetle (Pachymerus dactris) with those of the nut
(Manicaria saccifera) on which the beetles feed (176). The behavior
of these larvae is similar to that of rats (see Table II) in which dietary
myristic, as compared with lauric, acid is preferentially deposited.
Of the remaining land invertebrates may be mentioned the earthworm (Lumbricidae), which contains 1.2-1.3% of lipids, half of which
is unsaponifiable. The fatty acids are a third phosphatidic and form an
unusual range with Ci 0 to Ci 8 saturated and C 12 to above C 22 unsaturated (177).
2. Fats of Amphibians and Reptiles
The fatty acid composition of the depot fats of amphibians and of
reptiles forms a link between those of aquatic species and terrestrial
mammals. The extensive data reviewed by Hilditch (3) show that
among the amphibia and reptiles there is a wide range of variation,
from the depot fat of the frog with 15% C 20 -C 22 unsaturated acids and
11% palmitic acid to that of the crocodile with 27% palmitic acid and
only 4% C 20 -C 22 acids, corresponding closely to the proportions found
in the depot fats of mammals. These variations are, perhaps, more
closely related to the diet than to species, since Pathak and Pande (178)
found 12% of C 20 -C 22 unsaturated acids in the fats of the crocodile living on its natural diet of fish, as compared with 3.8% found by Gunstone
and Russell (143) in the fats of a captive crocodile fed on piglets.
F. B. SHORLAND
aquatic animals. However, this situation may arise from differences in
the dietary fat rather than from inherent differences between species.
1. Fats of Invertebrates
Hilditch (3) refers to the fatty acid composition of the depot fats of
six insects of the Orthoptera, the chrysalis oil of the silkworm and
the tent moth, as well as the larva fats of a few other groups. The composition of insect fats is variable. The saturated acids comprise 15-35%,
with palmitic acid as the main component. In accord perhaps with the
green-leaf diet, the unsaturated acids are mainly Ci 8 with linoleic and
linolenic acids often predominating. C 20 and C 22 unsaturated acids
appear to be generally absent but have been reported in substantial
amounts (26-44%) in the depot fats of two Mexican species (174, 175)
including the Mexican locust. The fatty acids from the latter, however,
failed to give the polybromide test for C 20 and C 22 highly unsaturated
acids. The fatty acids from the other Mexican insect gave ether-insoluble bromides which darkened at 200°. The evidence for the presence of polyunsaturated C 20 and C 22 acids in these insects is thus rather
inconclusive. The effect of the dietary fat is evident on comparing the
larva fats of the beetle (Pachymerus dactris) with those of the nut
(Manicaria saccifera) on which the beetles feed (176). The behavior
of these larvae is similar to that of rats (see Table II) in which dietary
myristic, as compared with lauric, acid is preferentially deposited.
Of the remaining land invertebrates may be mentioned the earthworm (Lumbricidae), which contains 1.2-1.3% of lipids, half of which
is unsaponifiable. The fatty acids are a third phosphatidic and form an
unusual range with Ci 0 to Ci 8 saturated and C 12 to above C 22 unsaturated (177).
2. Fats of Amphibians and Reptiles
The fatty acid composition of the depot fats of amphibians and of
reptiles forms a link between those of aquatic species and terrestrial
mammals. The extensive data reviewed by Hilditch (3) show that
among the amphibia and reptiles there is a wide range of variation,
from the depot fat of the frog with 15% C 20 -C 22 unsaturated acids and
11% palmitic acid to that of the crocodile with 27% palmitic acid and
only 4% C 20 -C 22 acids, corresponding closely to the proportions found
in the depot fats of mammals. These variations are, perhaps, more
closely related to the diet than to species, since Pathak and Pande (178)
found 12% of C 20 -C 22 unsaturated acids in the fats of the crocodile living on its natural diet of fish, as compared with 3.8% found by Gunstone
and Russell (143) in the fats of a captive crocodile fed on piglets.