. A manual of zoology. Zoology. IV. NEMERTINI 257 â pr widely distributed; statocysts are very rare. The excretory system consists of two tubes lying beside the lateral blood-vessels and connecting with branches terminating in flame ceUs, while they open separately to the exterior by one or several openings. As a rule the nemertines are dioecious, the gonads forming a row of lateral sacs, alternat- ing with the intestinal Ijlind sacs and opening dorsally. The development is sometimes direct, but usually a metamorphosis occurs in which a larva, the pilidium (or a reduced form of it, Desor's lar
. A manual of zoology. Zoology. IV. NEMERTINI 257 â pr widely distributed; statocysts are very rare. The excretory system consists of two tubes lying beside the lateral blood-vessels and connecting with branches terminating in flame ceUs, while they open separately to the exterior by one or several openings. As a rule the nemertines are dioecious, the gonads forming a row of lateral sacs, alternat- ing with the intestinal Ijlind sacs and opening dorsally. The development is sometimes direct, but usually a metamorphosis occurs in which a larva, the pilidium (or a reduced form of it, Desor's larva), appears. The pilidium is a helmet-shaped larva with, right and left below, a pair of lappets (fig. 237). The margins of lappets and helmet are ciliated, while at the top a bundle of longer cilia pro- ject from a thickened patch of ectoderm, the â¢Â¥=#â â s> ,Jm. Fig. Fig. 236. Fig. 237. 236.âAmphiporus ptilcher fafter Burger), a, alimentar)' canal; b, brain; c, ciliated groove; d, dorsal blood-vessel; /, lateral blood-vessel; m, retractor of proboscis; 11, lateral nerve cord; 0, ovary; p, poison sac; pn, protonephros; pr, proboscis; ps, pro- boscis sheath; r, rectum; 5, stylet of proboscis. Fig. 237.âPilidium lari'a (from Lang, after Salensky.) es, invaginations which later give rise to the nemertine skin; m, oral lobes; ind, archenteron; rn, ring nen'e; sp, apical plate; si, oesophagus; vtk, ciliated band. apical plate, which functions as a central nervous organ. Inside is the simple c£ecal archenteron, the mouth (blastopore) opening between the lappets. By a complicated process of growth and infolding this mesenteron becomes enclosed in a separate skin, produced from four inpushings (es); an anus is formed, and at the time of metamorphosis 17. 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 wo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
