Text-book of comparative anatomy . nervous system of the(Fig. 148) deserves special attention,distinctly marked supra - cesophagealglion or brain is wanting. The cesophagealring is very much elongated, in keepingwith the great length of the two limbs (cesophageal commissures),which run laterally in the prostomium (pro-boscis), arid which coalesce at its anteriorend, give off numerous branches towardsboth the exterior and interior; thosebranches which run dorsally inwards mayrepresent transverse commissures between thelimbs of the cesophageal ring. Below and be- FIG.
Text-book of comparative anatomy . nervous system of the(Fig. 148) deserves special attention,distinctly marked supra - cesophagealglion or brain is wanting. The cesophagealring is very much elongated, in keepingwith the great length of the two limbs (cesophageal commissures),which run laterally in the prostomium (pro-boscis), arid which coalesce at its anteriorend, give off numerous branches towardsboth the exterior and interior; thosebranches which run dorsally inwards mayrepresent transverse commissures between thelimbs of the cesophageal ring. Below and be- FIG. system ofhind the mouth the limbs of the cesophageal Echiurus, diagrammatic. s.«, The i f i •, two limbs of the a-sophageal ring, ring coalesce to form an unpaired ventral wMch join at the anterior end of Strand, which in adult animals has no gan- the prostomium and enter the ex- glion swellings, but is supplied with gang-Home treme anterior end of «ie ventral chord (Inn) behind the mouth ; nr,nerve rings; vb, anterior hooked. cells throughout its whole course; this strand runs in the ventral middle line on setEe;7l&. the two posterior circlesthe body wall to the posterior end of the of setfe; MI> n2> aPertures of the nephridia; a, anus. body, and gives off to the right and left at short intervals lateral branches which correspond with the rings of the outer integument. The corresponding right and left lateral 224: OOMPAEA TIVE ANA TOMY CHAP. branches pass into each other dorsally, and thus form in the body wall numerous consecutive nerve rings. The nervous system of the Myzostomidce (Fig. 149) is now very exactly known. It consists of an oesophageal ring surrounding the base of the pharynx, whose dorsal lateralportions are somewhat thickened, andso represent a weakly developed to the oesophageal ring lie gangli-onic cells. Further forward in thepharynx a second nerve ring (pharyn-geal ring) is found, which is connectedwith the oesophageal ring by several
Size: 896px × 2790px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
