. Bonner zoologische Monographien. Zoology. «. pm B : Schematic line drawings showing the ontogenetic origin of different coelomic spa- ces. A - Branchiostoma Icmceolatiim, after Prenant (1936); B - Branchiostoma floridae, after Holland et al. (1995). at - atrial cavity, co - coelom, epc - evaginating perivisceral coe- lom, gt - gonotome, mc - myocoel, mt - myotome, pc - perivisceral coelom, pm - pterygi- al muscle, sc - sclerocoel, st - sclerotome. partments should become pinched off from the dorsal mesodermal segments during the first two days of development (). The ventral part
. Bonner zoologische Monographien. Zoology. «. pm B : Schematic line drawings showing the ontogenetic origin of different coelomic spa- ces. A - Branchiostoma Icmceolatiim, after Prenant (1936); B - Branchiostoma floridae, after Holland et al. (1995). at - atrial cavity, co - coelom, epc - evaginating perivisceral coe- lom, gt - gonotome, mc - myocoel, mt - myotome, pc - perivisceral coelom, pm - pterygi- al muscle, sc - sclerocoel, st - sclerotome. partments should become pinched off from the dorsal mesodermal segments during the first two days of development (). The ventral part of the meso- derm surrounds the intestine and its cells constitute a solid mesoderm for most of the early development (Fig. 13, Plates 5 & 7). In the larval stages examined in this study, a coelomic gap is seen in the posterior third of the larvae in this ventral region (Plates 9, 15-17, Figs. 12 & 15). This space should become the perivisceral coelom of the adult (Prenant 1936, Holland, 1996). A sclerocoel is never present in the developmental stages examined in this study. Recent anatomical studies are ambiguous regarding the presence of a sclerocoel in adult cephalochordates. A coelomic cavity with the epithelial sclerothel is des- cribed by Holland & Holland (1990) and Ruppert (1997b). However, Ruppeit (1991, p. 9) states that "adult myomeres lack a cavity". This issue is in need of reinvestigation. The myocoel could be detected as a narrow intercellular space at the lateral side of most of the mesodermal segments (e. g., Fig. 10, Plates 5, 9, 14-18). Although. 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 Bonn, Zoologisches Forschungsinstitut und Museum Alexander Koenig
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