The common frog . of a great mass of jelly through *which dark specks (the yolks of the %%^ are ^%^, when microscopically examined, m^ay beseen to undergo a process of yolk subdivision andcleavage till a mulberry-like mass is formed. Uponthis soon appears the primitive groove/ whichforms a canal and develops beneath it a chordadorsalis according to the which has beenalready stated to be common to the whole of theVertebrata. Gradually the embryo assumes the form of a youngtadpole, and is provided with a pair of little holders(or organs for adhesion) just behind the mouth
The common frog . of a great mass of jelly through *which dark specks (the yolks of the %%^ are ^%^, when microscopically examined, m^ay beseen to undergo a process of yolk subdivision andcleavage till a mulberry-like mass is formed. Uponthis soon appears the primitive groove/ whichforms a canal and develops beneath it a chordadorsalis according to the which has beenalready stated to be common to the whole of theVertebrata. Gradually the embryo assumes the form of a youngtadpole, and is provided with a pair of little holders(or organs for adhesion) just behind the mouth, withsix openings on each side of the neck (Fig. 2, cl^-cl^),and with a pair of rudimentary external gills (Fig. 2, ^i i6 THE COMMON FROG. [CH.\P, b7^ and br^^). These openings are termed visceralclefts, which lead from the exterior into the throat,as already described. The solid pillars (or intervals)between the clefts, , the visceral arches, becomefurnished with gills,i or brauchicE, and are therefore cV rn. Fig. 2.—View of left side of Embryo Tadpole (after Parker), ^a-^ and /;, ^r-^t andsecond external branchiae ; cl^—cl^, the visceral clefis ; cp the left holder ;d, the olfactory organ : e, the eye : Ip, the left lip : Jn, the aperture of the mouth ;oJ>, the hinder margin of the rudimentary operculum. called branchial arches. The eggs are hatchedtowards the end of April, and the tadpole emergesin the stage represented at Fig. 3, 1. It has a rela-tively large head, a rounded body, and a long tail, bylateral undulations of which the little creature swimsabout. From behind the head, on each side, jut forthexternal branchiae as a small plume-like structure, butno limbs are visible. As the tadpole grows, the external plumose gillsat first greatly enlarge (Fig. 3, 2 and 2a), but after-wards become gradually absorbed, and are succeededby short gill filaments, which are developed alongeach of the branchial arches. These latter filaments 1 Gills (or branchise) are
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
