. A text-book of invertebrate morphology. Invertebrates. TYPE PBOTOORORDATA. 609 front of the anterior end of tlie paired ventral fin is the atrial pore (p), which leads into a cavity termed the atrium (6). The outer walls of this cavity arise as folds of the sides of the body, termed the epipleural folds, which, in- creasing in size, fuse together below except at the atrial pore, thus enclosing the atrial cavity (Fig. 279, b), which is lined throughout by ectoderm and surrounds the sides and ventral surface of the anterior two thirds of the body. Ante- riorly the cavity is closed by the fusio
. A text-book of invertebrate morphology. Invertebrates. TYPE PBOTOORORDATA. 609 front of the anterior end of tlie paired ventral fin is the atrial pore (p), which leads into a cavity termed the atrium (6). The outer walls of this cavity arise as folds of the sides of the body, termed the epipleural folds, which, in- creasing in size, fuse together below except at the atrial pore, thus enclosing the atrial cavity (Fig. 279, b), which is lined throughout by ectoderm and surrounds the sides and ventral surface of the anterior two thirds of the body. Ante- riorly the cavity is closed by the fusion of the folds with the body-wall in the neighborhood of the larval mouth, but in front of this is a hood-shaped fold which arises independ- ently of the atrial folds and forms the oral hood, at the bot-. Pig. 278.—AmpMoxus lanceolatus (after Boteri from Hertwig). a = anus. m — muscles. ail = eye. n = nephridium. b = atrial chamber. o — mouth. ch = notochord. p = atrial pore. g = reproductive organ. r = dorsal nerve-cord. I = liver. sp = branchial cleft. torn of which lies the original mouth, the margins of the hood surrounding what may be termed for distinction the adult mouth (Fig. 278, o). These margins are produced into a number of tentacular processes, termed cirrhi, each one of which contains an axial supportive rod borne by a skeletal ring surrounding the adult mouth, and each has its surface raised into numerous sensory papillae. The ectoderm is very simple in its character, consisting of a single layer of cells resting below upon a well-developed layer of connective tissue. The arrangement of the coelomic cavities is by no means simple, however, and may be best understood by considering their mode of development. In a very young embryo a fold may be seen extending along each side of the primitive digestive tract on its dorsal surface. In. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - c
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
