The porifera and coelentera . y hatched), mesogloea (a thick black line), andendodenn (lightly hatched), surrounding the coelenteron. and endoderm, and the coelenteron, are still represented. Thesecretion of a mesogloea, the perforation of a mouth, and the out-growth of tentacles, are the main morphological differences betweenembryo and adult hydroid. Hydroids are either solitary or colonial. The solitary forms,such as Hydra, are capable of reproduction by a process of budding(Braem, 15 ; Seeliger, 16), (Fig. 4, B), in which a part of the bodywall, enclosing coelenteric cavity, protrudes later
The porifera and coelentera . y hatched), mesogloea (a thick black line), andendodenn (lightly hatched), surrounding the coelenteron. and endoderm, and the coelenteron, are still represented. Thesecretion of a mesogloea, the perforation of a mouth, and the out-growth of tentacles, are the main morphological differences betweenembryo and adult hydroid. Hydroids are either solitary or colonial. The solitary forms,such as Hydra, are capable of reproduction by a process of budding(Braem, 15 ; Seeliger, 16), (Fig. 4, B), in which a part of the bodywall, enclosing coelenteric cavity, protrudes laterally; this elon-gates and forms a mouth and tentacles at its distal end ; the littleHydra, thus produced, becomes constricted off by an ingrowth of cells,which seal up both its central end and the body wall of the parent. THE HYDROMEDUSAE A process of budding, similar in character but not followed bya separation of progeny from parent, results in the production ofcolonial forms (Figs. 16 to 20); in the colony thus formed, the. Fio. c. 5.—Section of a medusoifl, plaowl mouth uijwards for coiiii>arison with a hydioid (Fig. 4).Tlie right half of the section is taken alon^ a radial canal, the left half between two radialcanals. CC, circular canal ; El\ exninbral surface ; C, ^onad or ncrative cells lying in theectoderm of a ])r(Xess of the subunibral Ixxly wall (characteristic of Leptomedusae); G,gonad lying in the ectodenn of the manubrium (characteristic of Anihoniedusae); 01., gastrallamella ; M, manubrium ; Nil, the outer, and .N7f, the inner jiarts of the nerve ring ; UC, radialcanal; SI, subunibral cavity; 7, tentacle; V, velum. Body layers represented as inFig. 4. tJ.—Section of a me<lusoid, at right angles to Fig. 5. Letters as in Fig. 5 ; Ixxly layers as inFig. 4. 7.—Diagram showing the chief radii of a medusoid. P, perradii (the first four radiiaccentuated in development); /, interradii ; A, adradii. coelenteron of each hydroid communicates with those of all t
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
