The microscope and its revelations . the congress of 624 a:nnulosa, or woems. two, each impregnating the ova of the other, seems to begenerally necessary. The ovaria, as in the Entozoa, extend through a large partFig. 273. of the body, their ramifications pro-ceedhig from thetwo oviducts {k, k),v/hich have a dila-tation (J) at theirpoint of is much ob-scurity about thehistory of the em-bryonic develop-ment of these ani-mals ; and the factsobserved by Sieboldseem to be best ex-plained upon the hy-pothesis, that whathas been usuallyconsidered as an Qggis really an egg-capsule cont
The microscope and its revelations . the congress of 624 a:nnulosa, or woems. two, each impregnating the ova of the other, seems to begenerally necessary. The ovaria, as in the Entozoa, extend through a large partFig. 273. of the body, their ramifications pro-ceedhig from thetwo oviducts {k, k),v/hich have a dila-tation (J) at theirpoint of is much ob-scurity about thehistory of the em-bryonic develop-ment of these ani-mals ; and the factsobserved by Sieboldseem to be best ex-plained upon the hy-pothesis, that whathas been usuallyconsidered as an Qggis really an egg-capsule containingseveral embryoeswith a store of sup-plemental yolk, asin Fwjmra (§ 351),which yolk is swal-lowed by the em-bryoes at a veryearly period of theiidevelopment vdthinthe capsule. Aftertheir emersion fromthe capsule, theembryoes bear sostrong a resem-blance to certainInfusoria, as to haveled Prof. Agassiz tothe conclusion, that the genera Paramecium and Kolpoda arenothing else than Pianarian larvse (§ ^QQ,note). This point, how-. Stnicture of Folycelis levigatus (a Planarianworm):—a, mouth, surrounded by its circularsucker; h, buccal cavity; c, oesophageal orifice;d, stomach; e, ramifications of gastric canals ;/, cephalic ganglia and their nervous filaments;g,g, testes; h, vesicula seminalis; i, male genitalcanal; k, k, oviducts ; I, dilatation at their pointof junction; m, female genital orifice. PLAXASIANS :—AXXELIDA. 625 ever, is still a matter for investigation.* TliePlanarise, however,do not multiply by eggs alone; for they occasionally undergospontaneous fission in a transverse direction, each segment be-coming a perfect anunal; and an artificial division into two oreven-more parts may be practised with a like result. In fact,the power of the Planariae to reproduce portions which havebeen removed, seems but little inferior to that of the Hydra(§ 301); a circumstance which is peculiarly remarkable, whenthe much higher character of their organization is borne inmin
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