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Show 1891.] TADPOLES OF THE EUROPEAN BATRACHIANS. 597 (Actes Soc. Linn. Bord. xxxi. 1876, p. 95, and Rev. Intern. Sc. ii. 1878, p. 488) belongs the credit of realizing its full systematic importance. W e are indebted to Goette (Entwick. d. Unke, p. 676, pi. xviii., 1875) and to Heron Royer (Bull. Soc. Zool. France, 1887, p. 645), who watched the process of its formation, for a correct understanding of its structure. 4. The Anus.-The anal tube is median, and opens on the middle line of the tail in tadpoles of most Batrachians (fig. 2, B, an.). In Rana and Hyla (fig. 2, A, an.), however, it is twisted to the right, opening in the former genus close to the lower edge of the lower caudal crest, higher up on the right side of the crest in the latter. It is not long since that this difference in the position of the anus was first observed. Goette (Entwick. d. Unke, p. 677, 1875) fancied that the dextral anus constantly accompanies the sinistral spiraculum, and his error has recently been repeated bv Spengel (Zool. Anz. 1888, p. 339). But I showed in 1884 (Ann. & Mag. N. H. xiv. p. 390), and again in 1886 (Bull. Soc. Zool. France, 1886, p. 319), that such a correlation exists only in the genera Rana and Hyla, the Toads and Pelobatoids having the median anus together with the sinistral spiraculum. 5. The Lines of Muciferous Crypts.-All tadpoles are provided with these organs, the hornologues of the lateral line in fishes. Their existence, long overlooked, and their signification as organs of a special sense, were first pointed out by F. E. Schulze (Arch. f. Anat. u. Phys. 1861, p. 767), whose researches into their structure were supplemented by himself (Arch. f. mikr. Anat. vi. 1870, p. 62), Leydig (N. Acta Ac. Leop.-Carol. xxxiv. 1868, p. 46), and Malbrane (Zeitschr. f. wiss. Zool. xxvi. 1875, p. 24). For further notes on the disposition of these lines we are indebted to Lessona (Atti Ace. Lincei, 3, i. 1877) and Lataste (Actes Soc. Linn. Bord. xxxii. 1879, p. 308). The latter author, however, overrated the systematic importance which is to be attached to these organs. It is a fact that they may differ greatly as regards their degree of development in individuals of the same species, and their arrangement also varies, within certain limits, irrespective of the species. I have found them usually most distinct in Pelodytes, Rana agilis, R. latastii, and Bombi-nator igneus, least in Bufo. The most distinct and constant appear to be the lines situated on the head, passing between the nostrils and bordering the eyes. I append figures (fig. 3, p. 598) of tadpoles of Rana agilis, Pelodytes punctatus, and Alytes obstetricans, in which these organs are represented by dotted lines. In addition to these lines all tadpoles show more or less distinctly a small whitish gland in the middle of the head between the eyes, the so-called frontal gland (Stieda, Arch. f. Anat. u. Phys. 1865, p. 52 ; Lessona, Atti Ace. Tor. v. 1880, p. 581 ; H . de Graaf, Bijdr. tot de Kenn. v. d. Bouw e. d. Ontwikk. d. Epiphyse b. Rept. e. Amph., Leyden, 1886), and a glandular streak, extending from the nostril towards the eye, the lachrymal gland (Born, Morph. Jahrb. ii. 1876, p. 611, figs. 23 &24). 6. Pigmentary Network.-In addition to the ordinary pigment- |