We may conclude, therefore, that they were preceded, in Cambrian times or earlier, by Arthropods possessing well developed appendages on all the trunk-segments.
Among the Hexapoda, as in Arthropods generally, the egg is large, containing an accumulation of yolk for the nourishment of the growing embryo.
Of such Arthropods the living Symphyla--of which the delicate little Scutigerella is a fairly well-known example--give us some representation.
In the Chaetopoda the head is formed of a praeoral lobe and of the oral segment; while in Arthropods a somewhat variable number of segments are added behind to this primitive head, and form with it what may be called a secondary compound head.
Thus the central nervous system of Arthropods must not be homologised with the central nervous system of Vertebrates, for it develops in a different manner.
So, too, the brain of Arthropods or of Mollusca is not strictly comparable with the brain of Vertebrates.
At first sight there seems here a contradiction of the principle of connections, for the appendages in Arthropods are lateral, whereas the paired bones of the vertebra are dorsal and ventral.
The relation of the organs to the external tube is of course different in Arthropodsand Vertebrates, but this is no contradiction of the principle of connections.
So, too, it is through function-change that certain of the ambulatory appendages of Arthropods have become transformed into jaws--their function as graspers of food has gradually prevailed over their main function as walking limbs.
In following out the development of the appendages he noticed how much alike were jaws and legs in their earliest stage, and how this supported Savigny's contention that the limbs of Arthropods belonged to one single type of structure.
We have seen that in Arthropods the body of the vertebra (cycleal) forms the open ring of the segment, which lies immediately under the skin, the vertebral tube coinciding with the epidermal tube.
The exact way in which Geoffroy homologised the parts of the appendages in Arthropods with the paired pieces of the typical vertebra is best shown by the reproduction of his figure of an abdominal segment of the lobster (Fig.
He considered that the mandibles and first maxillæ of Arthropods were the homologues of the upper and lower jaws of Vertebrates, adducing as confirmatory evidence the fact that in snakes the rami are separate.
He recognised that the body of Arthropods was made up of a series of similar rings, and that even the compact head of insects consisted of fused segments.
The masticatory organs of Arthropods were jaws disjointed at their symphysis; antennæ, nostrils turned outside in.
We have seen that the arthropods were the first of all animals to conquer the realm of the air, the earliest insects appearing in the Ordovician.
The vertebrates had now followed thearthropods and the mollusks upon the land, and developed a higher type adapted to the new environment.
The evolution of the arthropods and their relatives, with especial reference to insects.
What has become of the nerve-ganglion of the prostomial lobe of the Chaetopod in Peripatus is not clearly ascertained, nor is its fate indicated by the study of the embryonic head of other Arthropods so far.
The structure of the head in Arthropods presents three profoundly separated grades of structure dependent upon the number of prosthomeres which have been assimilated by the prae-oral region.
Arthropods and Chaetopods, but in many respects subject to peculiar developments--is observed.
A satisfactory consideration of the structure of the Arthropods demands a knowledge of what may be called the laws of metamerism, and reference should be made to the article under that head.
Arthropods and to the Mollusca, and the modern theory of the coelom was finally established.
In other Arthropods the cerebral ganglia arise in a similar way, but the invaginations disappear in the adult.
It sometimes happens that in Arthropods the egg breaks up into masses, which cannot be said to have the value of cells, as they are frequently without nuclei.
The word was generally adopted, and was applied alike to the blood-containing body-cavity of Arthropods and to the body-cavity of Vertebrata and segmented worms, in which there is no blood.
Defn: A class of marine arthropods in which the body is small and thin, and the eight legs usually very long; -- called also Pantopoda.
Defn: An extensive division of arthropods comprising all those which breathe by tracheæ, as distinguished from Crustacea, which breathe by means of branchiæ.
Defn: Any one of numerous species of extinct arthropods belonging to the order Trilobita.
Cloudsley-Thompson (1955a) cited cockroaches as one of the arthropods that scorpions feed upon.
Ectoparasites and other arthropods occurring in Texas bat caves.
These flies larviposit on the cockroaches, crickets, and possibly other arthropods that are flushed from cover by the ants.
Kohls and Jellison (1948) listed no cockroaches among the arthropods from six bat caves in Texas.
Ecological studies of the arthropods associated with certain decaying materials in four habitats.
Stratification ofarthropods in a wet stump cavity.
In the earliest fossiliferous rocks the most abundant and importantArthropods are the Trilobites (Fig.
They conduct limited entomological surveys to determine the existence of disease-vectoring arthropods in the AO.
The appearance of diseases orarthropods not known to exist in the AO are indicators that BW agents have been used.
If the arthropods include vectors of disease there would be a serious increase in disease hazards.
The area surrounding the storage facility is examined for the presence of animals, rodents, birds, and arthropods acting unusual, or dead in unusual numbers.
The normal balance between arthropods and birds that prey upon them in a given area may be severely upset, producing a marked overgrowth of the arthropods.
If there is an increase in arthropods that destroy vegetation there would be a serious destruction of food crops.
These appendages of arthropods are divisible into distinct limb-segments, separated from one another by moveable joints, and acted upon by special muscles.
The common ancestor of all the various arthropods which are found living on the earth to-day, was probably composed of a series of segments each very similar to the last and each bearing a pair of very similar appendages.
Aristotle had included in one class "Entoma" the six-legged arthropods which form the modern zoological class of the Hexapoda or Insecta, besides the Arachnida, the centipedes and the millipedes.
Nevertheless, it must not be overlooked that poisonous forms do exist, and they must receive attention in a consideration of the ways in which arthropods may affect the health of man.
The names printed in BOLD FACED TYPE indicate the hominoxious arthropods which have been most commonly mentioned in literature.
A number of other nematode parasites of birds and mammals have been reported as developing in arthropods but here, as in the case of the cestodes, experimental proof is scant.
Some amphibians and arthropods must spend at least part of their lives in the water.
Arthropods and snakes come to the pavement to warm themselves.
An extinct order of arthropods comprising the trilobites.
It should be noted, too, that the sense organs of arthropods are well developed, most of them being supplied with complex eyes, hearing organs, and highly sensitive feelers.
The body of Arthropods is made up of a chain of segments, all of which are built up on one common pattern, and each one is surrounded by a ring of the hardened skin or exo-skeleton that gives attachment to a pair of appendages.
The mental symphysis and pectoral girdle would prevent ingestion of an object much larger than the skink's body diameter, but soft-bodied and flexible arthropods of body diameter approximately equal to that of the skink may be ingested.
Arthropods which have recently undergone ecdysis and have the exoskeleton still thin and soft are no doubt digested much more completely than those that have more heavily sclerotized parts.
On the Reservation both opossums and skunks were, in many instances, attracted to the reptile traps by the insects and other arthropods in them, rather than by lizards.
The vertebrates had now followed the arthropods and the mollusks upon the land, and had evolved a higher type adapted to the new environment.
Leydig inarthropods 'Punktsubstanz,' and known in vertebrates and in invertebrates at the present time as 'neuropil.
All the known cases of inversion among arthropods occur in eyes, the retina of which is simple, and are all natural consequences of the process of invagination by which {114}the retina is formed.
Succeeding this prosoma or masticatory region, there occurs in all gill-bearing arthropods a respiratory region, in many cases more or less distinctly defined, which has received the name of mesosoma.
Also the worm-like ancestors of the arthropods almost certainly possessed a ciliated intestine.
Before concluding this chapter we shall take up the salient points in the geological history of Arthropods which constitute the highest subkingdom of all animals except the Vertebrates.
Thus metamorphosis occurs in this branch as well as among the Arthropodsand Echinoderms.
The Arthropods are animals of a high degree of organization.
The internal organs of the Arthropods show a more or less obvious segmentation corresponding with the segmentation of the body-wall.
The evolution of the arthropods reaches its culminating point in the insect, and in particular in the hymenoptera, as that of the vertebrates in man.
The arthropods in general were provided with a carapace; most of them were crustaceans.
To define these powers, we must consider, in the evolution both of the arthropods and the vertebrates, the species which mark the culminating point of each.
A glance at the nervous system of the arthropodsand that of the vertebrates shows us the difference.
Probably arthropods and vertebrates were threatened with it too.
Of what substance is the exoskeleton of arthropods composed?
Give the classes of arthropods with an example of each.
But between arthropods and vertebrates we can not yet clearly see a common origin, although there doubtless was such.
As we shall see hereafter, the relation of skeleton and muscle in arthropods is exactly the reverse.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "arthropods" in a variety of sentences. We hope that you will now be able to make sentences using this word.
