Twelve lectures on comparative embryology : delivered before the Lowell Institute, in Boston, December and January, 1848-9 / by Louis Agassiz ... Phonographic report, by James W. Stone ... Originally reported and published in the Boston Daily Evening Traveller.
- Louis Agassiz
- Date:
- 1849
Licence: Public Domain Mark
Credit: Twelve lectures on comparative embryology : delivered before the Lowell Institute, in Boston, December and January, 1848-9 / by Louis Agassiz ... Phonographic report, by James W. Stone ... Originally reported and published in the Boston Daily Evening Traveller. Source: Wellcome Collection.
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![nevertheless, exists. There is a circulation in In- sects which is only more generally overlooked.— The heart is a more elongated tube than in Crus- tacea, but it exists in all insects. It exists more developed in their larval condition, which shows that having a large heart in articulated animals, is , not characteristic of a higher structure; and how a great bulk of blood can be concentrated upon one point in Articulata, without assigning them a character of great eminence, is distincly shown, when we consider that in Worms, which undoubt- edly stand below the other two classes, there are as many as six, eight or more hearts, and in which the bulk of the blood is proportionally much great- er than in Crustacea or in Insects ; so that, the im- portance ascribed to the circulation of Crustacea, when this class was placed above Insects, I think vanishes before the consideration of the value of these characteristics, as noticed throughout the metamorphoses of Insects. A few words upon the subject of mastication and upon the chewing orders, will further show that Insects have to stand higher than other articu- lated animals. The chewing apparatus in Insects is a very complicated apparatus, so complicated that it is scarcely possible to give a correct idea of the arrangement of these parts, unless a person has become familiar with the objects themselves. I must, however, attempt to convey some idea of this apparatus. On the two sides of the head in those insects which are generally considered the highest, there are two large moveable pieces, mov- ing from right to left on the right side, and from left to right on the left side, in opposite directions horizontally. These parts are called mandibles. — Below these, is another pair of similar organs, moving also horizontally, which are often ser- rated, and to which are frequently added articu- lated appendages; these are called the maxilla.— These constitute two pairs of strong forcep-like jaws, very different, it seems, from any part in the In the diagram here, Jaws of Insects (Plate XVI. figs. A, B) your see the whole apparatus, first from a Beetle and a Grasshopper, (fig. C). Seen from above (fig. A) there is a kind of lip in sight, cov- ering the mandibles, and below, are the maxille; and below (tig. B) there is another kind of lip,keep- ing these in their respective positions. To the lower lip are also frequently appended articulated tentacles—the palpi. Fig.C. represents the maxille# of a Grasshopper seen in profile. we will have a strong mandible above; and some- what below and inward, the maxille; and farther below, we havethe lower lip. So that, between two horizontal continuous plates, called lips, there are moving forceps, the upper. called mandibles, and the lower maxilla. Then we have maxillary pal- pi. And to the lower lip there is another pair of palpi attached—the labial palpi. This is the structure of the jaws in all chewing insects. The Caterpillars have also such maxille as the perfect chewing insects, though not so com- plicated, to be sure, as in the most perfect Beetles, but nevertheless constructed in the same way,with a horny, powerful jaw, by which they chew the large quantity of food which they devour. Now this condition is changed in the Caterpillar during the pupa condition, when we have no longer such enlarged jaws; buta long sucker, j Plate XVI fig. D] consisting, however, of the same parts as in the chewing insects, only those parts which were mov- ing horizontally have become elongated, and with their margin have united, and instead of now mov- ing in that way, remain closed together, and form, a tube, a real sucker, through which, by the assist- into their stomachs. (The Professor here repre- sented, by means of his fingers, the jaws of the chewing insect, and the manner in which, by uni- ting, they can be transformed into a sucker.) Let the tube now be contractile and retractile,be- tween the upper and lower lip, and you have pow- erful jaws transformed into a narrow tube. It is a transformation which takes place with the other successive and progressive changes, so that we are entitled to consider such changes as also a pro- gress, if I am not mistaken; and to consider the condition of the insect in which he chews food, as the lower one, as it is the condition of the Larva; and the condition in which he sucks, to be the higher condition of the insect. And therefore, in principles derived from the study of Insects, and not from the study of other animals, judging of Insects by notions gained from that class, we shall consider those which suck their food, in which the jaws are elongated, those which pass through vari- ous metamorphoses, higher than those in which the jaws are placed horizontally—sharp cutting jaws,which devour large quantities of food. But this](https://iiif.wellcomecollection.org/image/b33278982_0066.jp2/full/800%2C/0/default.jpg)
