It presents a striking contrast to the simple Arthropod eye, where, in consequence of the existence of a dense exterior cuticle, the eye does not form a vesicle, and the lens is always part of that cuticle.
What is true of the dormant condition of arthropod life in the winter of the northern hemisphere is also true in a general way of that of the southern hemisphere at the same season of the year.
Having accepted these two conclusions, we formulate the generalization that tracheae can be independently acquired by various branches of Arthropod descent in adaptation to a terrestrial as opposed to an aquatic mode of life.
The Arthropod eye appears to be an organ of special character developed in the common ancestor of the Euarthropoda, and distinct from the Chaetopod eye, which is found only in the Onychophora where the true Arthropod eye is absent.
The corm becomes the seat of a development of a special visual organ, the Arthropod eye (as opposed to the Chaetopod eye).
The reduction of the outgrowth-bearing "corm" of the parapodium of either a Chaetopod or anArthropod to a simple cylindrical stump, devoid of outgrowths, is brought about when mechanical conditions favour such a shape.
This has proved to be a sound hypothesis and is now accepted as the basis upon which the Arthropod head must be interpreted (see Korschelt and Heider (3)).
The adhesion of a greater or less number of somites to the buccal somite posteriorly (opisthomeres) is a matter of importance, but of minor importance, in the theory and history of the Arthropod head.
The Arthropod head is a tagma or group of somites which differ in number and in their relative position in regard to the mouth, in different classes.
The comparison of theArthropod with the Vertebrate is extended also to the internal organs.
Turn the Arthropod on its back and the relative positions of the systems of organs are the same as in the Vertebrate.
The internal organs of the Arthropod are shown to stand in the same order to one another as in the Vertebrate, only the organs are inverted.
Audouin gave the detailed demonstration of this by his accurate and minute determination of the pieces of the arthropod skeleton.
The scats consist mainly of chitinous fragments of arthropod prey.
Slabs of bark clinging loosely to the tree trunks, with spaces beneath, provided shelter for the skinks and for the abundant arthropod fauna which probably constituted their chief food source.
My theory, then, makes the impossible assertion that what was hypoblast in the arthropod has become epiblast in the vertebrate, and what was epiblast in the arthropod has become hypoblast in the vertebrate.
In the arthropod this cephalic stomach leads into the straight narrow intestine; in the vertebrate the fourth ventricle leads into the straight narrow canal of the spinal cord.
Instances are seen in the Tunicata, and in various parasitic arthropod forms, such as Lernaea, etc.
The most primitive arthropod would appear to be one composed of exactly similar segments bearing exactly similar appendages, the segments of the appendages themselves all similar to one another.
It is highly improbable that this most primitive arthropod imaginable will ever be found, but after a survey of the whole phylum, it appears that the simpler trilobites approximate it most closely.
It is argued that the ancestral arthropod was a short and wide pelagic animal of few segments, which so far changed its habits as to settle upon a substratum.
In other words, without the arthropod host the disease-producing organism cannot complete its development.
In other cases, it is the asexual stage of the parasite which is undergone, and the arthropod then acts as the intermediate host.
As in the case of Spirochaeta duttoni, the organism is transmitted hereditarily in the arthropod vector.
There is the additional reason that these were the first cases known of arthropod transmission of pathogenic organisms.
Exterminate the arthropod host and the life cycle of the parasite is broken, the disease is exterminated.
Once anarthropod becomes an essential host for a given parasite it may disseminate infection in three different ways: 1.
This distinction is often overlooked and all the cases incorrectly referred to as those in which the insect or other arthropod acts as intermediate host.
Most operational rations are packaged in metal containers, or encased in heavy aluminum laminated plastics that can withstand boiling water; also, they are impervious toarthropod penetration.
At that ancient epoch not only were the vertebrate, molluscous, and arthropod types distinctly and clearly differentiated, but highly developed forms had been produced in each of these sub-kingdoms.
But the same may be said of every single arthropod and annelid if it be meant that all these organs are not contained in every possible slice.
A review of the facts of Arthropod development led Balfour[193] to conclude that the whole of the Arthropoda cannot be united in a common phylum.
The morphologist would derive all the varieties of Arthropod segments from the very simple and uniform chitinous cuticle found in Annelids and many Insect-larvæ.
A pair of limbs may next be inserted between the terga and sterna, and the simple segment thus composed occurs so extensively in the less modified regions and in early stages that it may well be considered the typical Arthropod somite.
The primitive structure of the Arthropod limb is adapted to locomotion in water, and persists, with little modification, in most Crustacea.
The integument of an Arthropod is stiffened by a deposit of the tough, elastic substance known as Chitin, which resembles horn in appearance, though very different in its chemical composition.
Coming to the Arthropod eye, fresh from his investigation of the vertebrate retina, Schultze found in the retinal rods of Insects the same lamellar structure which he had discovered in Vertebrata.
