. Biology and human life. Biology. BUTTERFLIES AND BEES 35 mouths, we shall again find many basic simi- larities in spite of the great differences. Among animals that are built on substan- tially the same plan the corresponding parts are said to be homologous. Thus, the thorax of one insect is homologous with the thorax of another insect. More- over, the thorax of a butterfly is said to be homologous with the three distinct segments immediately behind the head of the caterpillar. We may also say that the three pairs of legs on one insect are homol- ogous with each other, since they originate a
. Biology and human life. Biology. BUTTERFLIES AND BEES 35 mouths, we shall again find many basic simi- larities in spite of the great differences. Among animals that are built on substan- tially the same plan the corresponding parts are said to be homologous. Thus, the thorax of one insect is homologous with the thorax of another insect. More- over, the thorax of a butterfly is said to be homologous with the three distinct segments immediately behind the head of the caterpillar. We may also say that the three pairs of legs on one insect are homol- ogous with each other, since they originate and develop in the same way, in spite of differ- ences, as between the hind leg of the grass- hopper, for example, and the front legs. In the same way we con- sider the "balancers" of a fly homologous with the hind wings of the butterfly and the wing covers of the beetle homologous with the front wings. The idea of homology helps us to understand a certain same- ness among organs that appear to be very different in structure. Fig. 16. Homology in the appendages of the lobster In the Crustacea all the appendages are built on the same plan, but each segment of the body (rep- resented by Roman numerals) has a distinctive organ. I and // are sensory; III-V combine sen- sory functions with food-getting; VI-VIII are chiefly food-getters, but are also related to breath- ing; IX is the nipper; X and XI are both grasp- ing and locomotor organs; XII and XIII are walking legs. The abdominal appendages XIV- XVIII are called swimmerets and probably assist in slow swimming. XIV and XV are also related to reproduction in the male, and in the female all the swimmerets carry the hatching eggs and larvse. XIX and XX spread out into a flat tail-paddle, used in swimming backward suddenly. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble th
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Keywords: ., bookcentury1900, bookdecade1920, bookpublishe, booksubjectbiology
