A Student's Text-book of Zoology: Tunicata, Enteropneusta, Echinodermata, and Arthropoda. The introduction to Arthropoda, the Crustacea and Xiphosura by J. J. Lister. The Insecta and Arachnida by A. E. Shipley

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S. Sonnenschein and Company, Limited, 1909 - Zoology
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Page 567 - So far as I can judge, it is used as a defensive weapon ; but this of course will not exclude its offensive use. They will turn their heads to any part of the body which is being irritated and violently discharge their slime at the offending object. Locomotion is effected entirely by means of the legs, with the body fully extended. Of their food in the natural state we know little ; but it is probably mainly, if not entirely, animal.
Page 568 - ... pass into the oviducts about one month before the young of the preceding year are born. They are born one by one, and it takes some time for a female to get rid of her whole stock of embryos ; in fact, the embryos in any given female differ slightly in age, those next the oviduct being a little older (a few hours) than those next the vagina. The mother does not appear to pay any special attention to her young, which wander away and get their own food.
Page 551 - Guilding (No. 1), who first obtained specimens of it from St. Vincent in the Antilles. He regarded it as a Mollusc, being no doubt deceived by the slug-like appearance given by the antennae. Specimens were subsequently obtained from other parts of the Neotropical region and from South Africa, and the animal was variously assigned by the zoologists of the day to the Annelida and Myriapoda (vide Moseley, No 22, and Sclater, No. 41). Its true place in the system, as a primitive member of the group Arthropoda,...
Page 551 - This unlikeuess to other Arthropoda is mainly due to the Annelidan affinities which it presents, but in part to the presence of the following peculiar features: (1) the number and diffusion of the tracheal apertures, (2) the restriction of the jaws to a single pair, (3) the disposition of the generative organs, (4) the texture of the skin, and (5) the simplicity and similarity of all the segments of the body behind the head. The Annelidan affinities are superficially indicated in so marked a manner...
Page 567 - The young are born in April and May. They are almost colourless at birth, excepting the antennae, which are green, and their length is 10 to 15 mm. A large female will produce thirty to forty young in one year. The period of gestation is thirteen months, that is to say, the ova pass into the oviducts about one month before the young of the preceding year are born. They are born one by one, and it takes some time for a female to get rid of her whole stock of embryos ; in fact, the embryos in any given...
Page 559 - It is mainly characterised by the presence on the ventral border of definite transverse commissural fibres. THE SKIN. The skin is formed of three layers. 1. The cuticle. 2. The epidermis or hypodermis. 3. The dermis. The cuticle is a layer of about 0-002 mm.
Page 567 - I kept in cavity eagerly devoured the entrails of their fellows, and the developing young from the uterus. They also like raw sheep's liver. They move their mouths in a suctorial manner, tearing the food with their jaws. They have the power of extruding their jaws from the mouth, and of working them alternately backwards or forwards. This is readily observed in individuals immersed in water.
Page 560 - I shall call the tracheal pit (fig. 30), the walls of which are formed of epithelial cells bounded towards the lumen of the pit by a very delicate cuticular membrane continuous with the cuticle covering the surface of the body. The pits vary somewhat in depth ; the pit figured was about 0'09 mm. It perforates the dermis and terminates in the subjacent muscular layer.
Page 572 - D, 2). The last section of this tube retains its connexion with the ventral portion of the somite, and so acquires an external opening, which is at first lateral, but soon shifts to the middle line, and fuses with its fellow, to form the single generative opening. The praeoral somite develops the rudiment of a nephridium, but eventually entirely disappears. The jaw somite also disappears ; the oral papilla somite forms ventrally the salivary glands, which are thus serially homologous with nephridia.
Page 558 - XVIII, fig. 22 / ri) may be regarded as the anterior ganglion of the ventral cords. There are, 'therefore, -according to the above reckoning, nineteen pairs of ganglia connected with the ventral cords. The ventral cords are placed each in the lateral compartments of the body cavity, immediately within the longitudinal layer of muscles. They are connected with each other, rather like the pedal nerves of Chiton and the lower Prosobranchiata, by a number of commissures. These commissures exhibit a fairly...

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