. Zoology : for students and general readers . Zoology. 218 ZOOLOOT. side of the base of the yeluni (v) of the Pilidium ap- l^ear two thickenings of the skin, one pair in front, the other behind; these thickenings push inwards, and are the germs of the anterior and posterior end of the future worm. The anterior pair become larger than the posterior ; the part of the disk next to the oeso- phagus thickens ; at the same time the ahmentary canal of the Pilidium grows smaller, and only a narrow slit remains. The disks now divide into two layers, the outer much thicker than the inner. Soon the ante
. Zoology : for students and general readers . Zoology. 218 ZOOLOOT. side of the base of the yeluni (v) of the Pilidium ap- l^ear two thickenings of the skin, one pair in front, the other behind; these thickenings push inwards, and are the germs of the anterior and posterior end of the future worm. The anterior pair become larger than the posterior ; the part of the disk next to the oeso- phagus thickens ; at the same time the ahmentary canal of the Pilidium grows smaller, and only a narrow slit remains. The disks now divide into two layers, the outer much thicker than the inner. Soon the anterior pair of disks unite, and the head of the worm is soon formed, when the elliptical outline. Fig. 142.—Larra or "Pilidium" of Nemer- „f j--|,„ flnf wnrm i<? indi- tes, with tlie worm growing in it. v, velum ; "I ^'^^ ^^^ WOrm IS mUI After Leuc'kart*"°''°"'''^''''*°"°™'~ cated, and appears some- what as in Fig. 143. The yolk mass, with the alimentary canal of the Pilidium, is taken bodily into the interior of the Nemertes, the Pilidium-skin falls off, and the worm finally seeks the bottom. The free-swimming larvEe of other ISTemerteans are very closely similar to those of the Annelids, so that from this fact and the nature of the highly developed circulatory system, the Nemerteans have been removed from the neighborhood of the flat worms, and placed near the Balanoglossus and Gephyrea, as Avell as the leeches. Order 1. Anojjla.—In this group the pro- lloTttmI^ie±'"' l^oscis is without a style. The species of Lineus and ileckelia are, in some cases, very long. Meulcelia ingens Leidy is 2^ centimetres (an inch) wide, and attains a length of 4 metres (ISj feet). It. 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 Packard, A. S. (Alpheus Spring), 1839-1905.
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
