. Outlines of zoology. Fig. 220. — Male of Argo-nauta (after Jatta), show-ing hectocotylus arm;compare Fig. 9 of female. GENERAL NOTES ON MOLLUSCS. 411 female. There its discoverers described it as a parasitic worm, Hectocotylus. The lost arm is afterwards regenerated. In Sepia,however, the modified arm is not discharged, but is simply thrust intothe mantle cavity of the female. The spermatophores probably enterthe oviduct, and burst Fig. 221.—Bunch oi Sepia eggs attached to plant.—After Jatta. The eggs, when laid, are enclosed within separate black capsulescontaining gelatinous stuff,
. Outlines of zoology. Fig. 220. — Male of Argo-nauta (after Jatta), show-ing hectocotylus arm;compare Fig. 9 of female. GENERAL NOTES ON MOLLUSCS. 411 female. There its discoverers described it as a parasitic worm, Hectocotylus. The lost arm is afterwards regenerated. In Sepia,however, the modified arm is not discharged, but is simply thrust intothe mantle cavity of the female. The spermatophores probably enterthe oviduct, and burst Fig. 221.—Bunch oi Sepia eggs attached to plant.—After Jatta. The eggs, when laid, are enclosed within separate black capsulescontaining gelatinous stuff, but the stalks of the capsules are united, sothat a bunch of sea-grapes results. General Notes on Molluscs From the description of these three types a general ideaof the structurd of Mollusca may be obtained, but it shouldbe noted—(i) that all the three types are specialised; (2)that two small classes, the Solenogastres and the Scaphopoda,are unrepresented in the descriptions ; (3) that in the threeclasses to which the types belong there is much diversityof structure, this being especially true of the large andheterogeneous class of Gasteropods. In surveying the structure of the whole group, it is con-venient to begin with the most striking of the externalcharacters—the absence or presence of a well-developedhead region. In the Lamellibranchs or Pelecypoda the head is absent,and along with it the tentacles, the radula, and t
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
