Title Formation of Ganglions and Stomodaeum in Normal and Separate Embryos of Horseshoe Crab, Tachypleus tridentatus

The process offormation ofganglions and stomodaeum was examinedin normal embryo畠andseparateembryoswhosestomodaeadidnotpassthroughthemiddleofthenervoussystem・ Thefollowingfactswereestablished・1)Thestructureofthestomodaeumisrecognizableaftrestage14・ 2)Thecellmassesofganglionsareobservedclearlyafterstage16;thecommlSSureSareStainedbyeosin afterstage19・3)Thefinalnumberofganglionsissettledbystage19;thismeansthatthef。,m。ti。。。f SegmentPrimordiaissettledbystage19・4)Thestomodaeumpassesthroughtheareabetweenthe COmmissuTeOfthefirstprosomaticganglions(chelicerasegment)andthatofthesecondganglions.5) TheでrOSヲlngOfthestomodaeumandthenervoussystemisthoughttobeformedatstage18-19.6)The CrOSSlnglSCOnStruCtedduringtheclusteringofthecellscomposlngthebrain;thestomodaeumdoesnot determinethepathwayfortheclusteringofthesecells・7)Thepositionofthemouthisnotappropriate asanindicatorfordeterminationofhomologoYSSegmentSamOngarthropodanspecies・8)Thecrossing doesnotconstituteavalidreasonforreJeCtlngtheideathatDeuterostomiahaveorlglnatedfrom Protostomia.