. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. Fig. 223. Thread cells of Bdellosloma, one intact, the other ' exploded,' after Ayers. dorsals and caudal. The skin is without scales, but is rich in mucus-secreting cells, and in the myxinoids contains also nu- merous pockets of so-called thread cells, these pockets extending into the underly- ing muscles. These thread cells have their protoplasm converted into a long thread, and when these are dis- charged, the threads become unwound ; and these and the mucus are so abundant that one of these animals will convert a bucket
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. Fig. 223. Thread cells of Bdellosloma, one intact, the other ' exploded,' after Ayers. dorsals and caudal. The skin is without scales, but is rich in mucus-secreting cells, and in the myxinoids contains also nu- merous pockets of so-called thread cells, these pockets extending into the underly- ing muscles. These thread cells have their protoplasm converted into a long thread, and when these are dis- charged, the threads become unwound ; and these and the mucus are so abundant that one of these animals will convert a bucket of water into a thick jelly. The mouth is at the bot- tom of a more or less circular suctorial funnel, the inside of which, like the tip of the mobile tongue, is armed with horny, cuticular teeth, which aid the suckers in anchoring these animals to the fish on which they feed, and also serve to rasp the flesh. The alimen- tary canal is straight ; a cir- cular fold, the velum, occurs inside the mouth ; no cloaca is present. The brain has well- developed cerebral lobes which may be solid or hollow, but the cerebellum is very small. The nasal organ is median, and is placed at the posterior side of the hypophysial duct, the opening to which thus serves as the nostril, opening either at the tip of the snout (myxi- noids) or upon the top of the head (petromyzontes). The. Fig. 224. Brain and nasal organ of Petromyzon. In front is (darker) the nasal canal, behind which are the plaits of the nasal membrane. On either side of the twixt brain are bits of the cartilage of the chondrocranium, and farther back the otic capsules. deeper end of the hypophysis expands into a large sac, which. 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 the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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