Text-book of comparative anatomy . with tentacle, taster with or without sensory filament, or isolatedbracts. This dispersed arrangement is to be explained in this way : theparts belonging to a sterile person, such as siphon or taster, bract ortentacle, become detached, and move away from each other, and stand VOL. I I 114 COMPARATIVE ANATOMY CHAP. separately on the stem. These dislocated portions or organs are ableto multiply independently. II. The Diseonanthe (Disealia, Porpeta, Porpalia, Velella).— These have to be interpreted quite differently from the SiphonantJn:According to the harmonio
Text-book of comparative anatomy . with tentacle, taster with or without sensory filament, or isolatedbracts. This dispersed arrangement is to be explained in this way : theparts belonging to a sterile person, such as siphon or taster, bract ortentacle, become detached, and move away from each other, and stand VOL. I I 114 COMPARATIVE ANATOMY CHAP. separately on the stem. These dislocated portions or organs are ableto multiply independently. II. The Diseonanthe (Disealia, Porpeta, Porpalia, Velella).— These have to be interpreted quite differently from the SiphonantJn:According to the harmonious and convincing teaching of ontogeny andcomparative anatomy, these animals must be considered as MedusceAvith marginal tentacles. These Medusce have a gastric tube withmouth (principal siphon) in the centre of the subumbrella in thetypical way, but also produce secondary siphons or palpons, by gemma-tion, on the subumbrella (just as in the Gastrollasta); out of thewall of these secondary siphons the Medusa-shaped gonophores Ik. gm PIG. 87.— Porpalia prunella, after Haeckel. cd, Central gland; Ik, air chamber; cp, centralpore of the same ; rk, radial canal; sp, supporting plate ; eu, exumbrella ; su, subumbrella ; t, ten-tacles ; g, gonades; o, mouth ; ms, principal siphon ; gm, accessory siphons. bud (Fig. 87). All the tentacles belong to the margin of the un-divided persistent Medusa umbrella. In the umbrella (on which inVcldla a vertical crest, generally placed diagonally, rises) an airvesicle is developed on the exumbrellar side; this is often of very com-plicated structure, many chambered, and originally octoradiate; thechambers communicate with the exterior through numerous young stages of the Diseonanthe are typical Medusa!, with 8 (later16) tentacles at the disc margin, and with one central gastric peduncleor siphon. The gonophores detach themselves as free-swimmingmedusoid sexual persons, and onty ripen the sexual products after theirseparation. The view
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
