PROF. E. BAY LANKESTEE ON LEPIDOSIEEN AND PEOTOPTEEUS. 17 



The form and ornamentation of the scales have been more or less fully described 

 by Natterer and Bischoff in Lepidosiren, by Owen in Frotopterus, and by Giinther 

 in Ceratodus. From Wiedersheim we have a more minute account of the denticles 

 which are set on the polygonal arese marking the scales of Frotopterus. In PL II. 

 figs. 4-9, I have reproduced drawings prepared for me by Mr. E. S. Goodrich, F.L.S., of 

 Merton College, my assistant in the Oxford Museum, showing the relative size of the 

 scales in the three genera Ceratodus, Frotopterus, and Lepidosiren, and also showing 

 the denticulate ornament of the scales, equally magnified in each case for comparison. 

 The scale chosen in each case is taken from a point near the middle of the inter- 

 membral area, and about halfway between the dorsal and ventral mid-line ; the object 

 has been to select in each case a similarly-conditioned scale. It will be seen that the 

 scale of Ceratodus is enormous compared with those of the other two genera, and that 

 that of Frotopterus is larger than that of Lepidosiren. (See further, as to the scales, 

 in the note to the Explanation of the Plates.) 



The denticulations of the scales do not vary in size proportionately to the size of the 

 scales, but are only somewhat coarser in Ceratodus than in Frotopterus and Lepidosiren 

 (PI. II. figs. 7-9). 



The last point, in reference to the Paraguayan Lepidosiren, to which I desire to draw 

 attention in the present communication is the remarkable development of the villi on the 

 hind limbs. These were described and figured by me in outline in a letter to ' Nature ' 

 in April 1894. They have also been described, but not figured, by Prof. Ehlers in a 

 communication to the Gottingen ' Nachrichten,' 1894, p. 87, which was not published 

 until June, and was unknown to me when my letter in 'Nature' was published, 

 although some author's reprints had been distributed before that date. It appears 

 that these villi occur only on male specimens. They are present on all the male 

 specimens I have examined, and are absent from the females. They occur on the 

 postero-medial surface of the elongated pelvic fins, and are seen both in PI. II. fig. 1 

 and in the enlarged drawing of the limb (PI. II. fig. 3), which is represented as turned 

 forward so as to expose them fully to view. The villi are small, pale-coloured, blunt 

 processes, from three to four times as long as broad ; they are either simple or joined, 

 to the number of two, three, or four, on a common base. I have examined the micro- 

 scopic structure of these villi by means of transverse sections. They are covered with 

 epidermic cells, which are two or three deep, and show evidence, in the condition of 

 their nuclei, of being in course of active multiplication. But I did not observe any 

 special characters of interest in these cells; they were block-like, solid, and not 

 flattened. Below the epithehal ceDs is a finely fibrous connective tissue, which in 

 transverse section of the villi is seen to occupy the axis, and to take the form of trabeculse 

 enclosing oblong cavities with rounded contours. Numerous nuclei belonging to the 

 connective tissue — some in karyokinetic activity — are apparent in such sections, and 

 here and there a minute blood-vessel. The cavernous structure of the connective tissue 



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