1894.] YOUNG OF 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 Turners nomen- 

 clature, " macrosmatic " ; and Zuckerkandl describes eight ethmoid 

 turbinals in the middle line in this animal. In my 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 my 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 per- 

 forated, 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 " (" ISasenmuschel ") ex- 

 tends from near the anterior end of the nasal cavity backwards as far 

 as the fourth ethmoturbinal (fig. 3, m.tb.), 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 II. (fig. 15), a fold being visible even with the naked eye 

 along its middle part (fig. 3). The folding is much more compli- 

 cated 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 (veriistigte 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 Home in Ornithorhynchus. Zuckerkandl was unable 

 to observe this ; but I have satisfied myself that both Monotremes 



