. Bonner zoologische Monographien. Zoology. 35 - In the anterior part of the nephridium the ventral cells are differentiated into muscle cells which clasp the mouth opening (). - The posterior part of the organ consists of a narrow canal (). About five cells make up this short channel, which opens into the oral cavity. The cells bear prominent nuclei and possess mitochondria. Especially in the apical parts, nume- rous vesicles (either empty or with light, granulated contents) can be seen. The canal cells are interconnected by septate junctions and bear a single apical cilium. Pre
. Bonner zoologische Monographien. Zoology. 35 - In the anterior part of the nephridium the ventral cells are differentiated into muscle cells which clasp the mouth opening (). - The posterior part of the organ consists of a narrow canal (). About five cells make up this short channel, which opens into the oral cavity. The cells bear prominent nuclei and possess mitochondria. Especially in the apical parts, nume- rous vesicles (either empty or with light, granulated contents) can be seen. The canal cells are interconnected by septate junctions and bear a single apical cilium. Preoral pit (Figs. 15 & 18; Plates 10 & 11, A) The preoral pit is ontogenetically derived from the left diverticulum of Hatschek which is seen in the neurulae with ten and eleven segments (Plates 3 & 6). This diverticulum is sealed off from the anterior archenteron and retains, in contrast to its right counterpart, tall cells. The cells are in the beginning not distinguishable from the endodermal, polar, epithelial cells of the archenteron. The left diverti- clulum comes into contact with the epidermis and opens to the exterior as the pre- oral pit. An intermediary stage, where the process of migration could be docu- mented, was not observed. In the larval stage the preoral pit is an epithelially orga- nized structure lying dorsal to the oral papilla just in front of the relatively large left-sided mouth opening (Fig. 15; Plates 10 & IIA). It is a bean-like organ situa-. : Transmission electron micrograph of the preoral pit of a larva of Brauchiostoma lanceolatum (11 Oh pf, 18°C). Note the rostral coelom at the left comer of the micrograph. Inset: septate junction connecting two preoral pit cells apically. ci - cilium, ct - coelothel. ecm - extracellular matrix, nc - notochord, nu - nucleus, RC - rostral Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appeara
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Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectzoology
