. Outlines of zoology. Zoology. CCELENTERA, compared with Ilydrozoa, in the possession of an ectodermal gullet [see footnote on page 146), but differ in possessing ectodermal septal muscles and in some histological features. Among those closely allied to Aitrelia^ some, , Felagia, have a direct development without the intervention of Scyphistoma or Strobila stages, but this may occur exceptionally in Aiirelia. Cyanea is often very large, " it may measure y-^- feet across the bell, with tentacles 120 feet ; Chrysaora is hermaphro- dite, and has diffuse sperm sacs even upon th
. Outlines of zoology. Zoology. CCELENTERA, compared with Ilydrozoa, in the possession of an ectodermal gullet [see footnote on page 146), but differ in possessing ectodermal septal muscles and in some histological features. Among those closely allied to Aitrelia^ some, , Felagia, have a direct development without the intervention of Scyphistoma or Strobila stages, but this may occur exceptionally in Aiirelia. Cyanea is often very large, " it may measure y-^- feet across the bell, with tentacles 120 feet ; Chrysaora is hermaphro- dite, and has diffuse sperm sacs even upon the arms. In the Rhizostomce—e-g--, Cassiopeia and Pilema^ the mouth is obliterated, and replaced by numerous small pores on the four double arms. Lucernaria and its allies are interesting sessile forms which have been compared to sexual Scyphistomas—that is, are regarded as persistently larval forms. Cojitrast between Hydi-ozoon a?id Scyphozoon Fig. 45.—Lucernaria. {After KOROTN'EFF.) Hydrozoon (Craspedota.) small swimming The majority are ; A flap or velum (craspedon) projects i wards from the margin of the bell. No tEcniolEe, nor gastric filaments. A double nerve ring around the margin. Naked sense organs either optic or audi- tor>'. They are usually derived from the skin, but the auditory sacs may be modified tentacles. Reproductive organs on the radial canals or by the side of the manubrium. The reproductive cells are usually derived from the ectoderm. With the exception of the Trachymedusse, all arise as the liberated reproductive persons of Hydroid coloTiies. True Hydrozoa. SCVl'HOZOON. (ACRASPEDA.) Many are large "jelly ; No velum. (The vclarimn of Aurclia is a mere fringe, \-eiy inconspicuous in the adult, and not inturned.) In the Scyphistoma there are four tasniolje, from pari of which the gastric fila- ments of the adult grow. Eight separate nervous centres beside the sense organs, and a sub-umbrellar nervous plexus. Sens
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
