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Show 1894.] YOUNG OE ECHIDNA ACULEATA. 9 adaptation to its aquatic habits. Symington, however, thought he could recognize five, the number characteristic of most osmatic mammals, and therefore describes Ornithorhynchus as " micros-matic." Echidna, on the other hand, is, to use Turner's nomenclature, " macrosmatie " ; and Zuckerkandl describes eight ethmoid turbinals in the middle line in this animal. In m y younger stage I could only recognize six, and in the older seven, which are easily seen, and probably a smaller eighth behind these (fig. 3). The sphenoidal sinus is represented by a shallow groove. In Stage I. the six ethmoid turbinals appear in m y dissection as simple lobes, all being at about the same level and not reaching the septum nasi. Sections, however, show that some, at any rate, are becoming subdivided (fig. 11). In Stage II. this subdivision into secondary lobes has gone still further, the second to the sixth exhibiting distinct folds (fig. 3 ) ; and in transverse sections a considerable complication is seen. In the adult this branching is carried further still, so that in the dry skull about the posterior half of the nasal chamber is filled with a complicated mass of spongy bones (compare pi. i. fig. 3 of Zuckerkandl's memoir) : from the fifth backwards these do not extend so far towards the median line as the others, on account of the folds on the septum nasi in this region, between which the turbinals extend. The proper olfactory region of the nasal chamber is thus very largely developed, and the cribriform plate is especially large, and perforated, as in all mammals but Ornithorhynchus. The first ethmoid turbinal (so-called " naso-turbinal") is a simple plate extending forwards some distance beneath the nasal bone (figs. 3 & 15, e.tb.1), with which it becomes united in the adult. The 7th (and ? 8th) are also quite simple in Stage II. A sensory and ciliated epithelium covers all these except the " naso-turbinal." In Stage I. a simple "maxillo-turbinal" ("Nasenmuscbel") extends from near the anterior end of the nasal cavity backwards as far as the fourth ethmoturbinal (fig. 3, m.ib.), narrowing off gradually posteriorly as well as anteriorly. Sections of Stage I. show that it has the form of a ridge, which is beginning to become branched (figs. 10 and 11), the branching being carried much further in Stage IT. (fig. 15), a fold being visible even with the naked eye along its middle part (fig. 3). The folding is much more complicated in the adult, and from a comparison with the skeletal parts of an adult E. spinosus the maxillary turbinal apparently belongs to the folded (" gefalteten " ) , and not to the doubly-coiled (" doppelgewundenen ") variety, as stated by Zuckerkandl; while in Ornithorhynchus, according to Symington, it " constitutes a well-marked example of the branching variety (verastigte Muschel)," though Zuckerkandl describes it as a " gefaltete Nasenmuschel." The epithelium covering this turbinal is, as usual, non-sensory, resembling that lining the general nasal cavity, and bearing cilia. A communication between the two nasal cavities has been described by H o m e in Ornithorhynchus. Zuckerkandl was unable to observe this ; but I have satisfied myself that both Monotremes |
